diff --git a/solidity/contracts/hooks/ArbL2ToL1Hook.sol b/solidity/contracts/hooks/ArbL2ToL1Hook.sol
new file mode 100644
index 0000000000..488dabc1ee
--- /dev/null
+++ b/solidity/contracts/hooks/ArbL2ToL1Hook.sol
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+pragma solidity >=0.8.0;
+
+/*@@@@@@@       @@@@@@@@@
+ @@@@@@@@@       @@@@@@@@@
+  @@@@@@@@@       @@@@@@@@@
+   @@@@@@@@@       @@@@@@@@@
+    @@@@@@@@@@@@@@@@@@@@@@@@@
+     @@@@@  HYPERLANE  @@@@@@@
+    @@@@@@@@@@@@@@@@@@@@@@@@@
+   @@@@@@@@@       @@@@@@@@@
+  @@@@@@@@@       @@@@@@@@@
+ @@@@@@@@@       @@@@@@@@@
+@@@@@@@@@       @@@@@@@@*/
+
+// ============ Internal Imports ============
+import {AbstractPostDispatchHook} from "./libs/AbstractMessageIdAuthHook.sol";
+import {AbstractMessageIdAuthHook} from "./libs/AbstractMessageIdAuthHook.sol";
+import {Mailbox} from "../Mailbox.sol";
+import {StandardHookMetadata} from "./libs/StandardHookMetadata.sol";
+import {Message} from "../libs/Message.sol";
+import {TypeCasts} from "../libs/TypeCasts.sol";
+import {IPostDispatchHook} from "../interfaces/hooks/IPostDispatchHook.sol";
+import {MailboxClient} from "../client/MailboxClient.sol";
+
+// ============ External Imports ============
+import {Address} from "@openzeppelin/contracts/utils/Address.sol";
+import {ArbSys} from "@arbitrum/nitro-contracts/src/precompiles/ArbSys.sol";
+
+/**
+ * @title ArbL2ToL1Hook
+ * @notice Message hook to inform the ArbL2ToL1iSM of messages published through
+ * the native Arbitrum bridge.
+ * @notice This works only for L2 -> L1 messages and has the 7 day delay as specified by the ArbSys contract.
+ */
+contract ArbL2ToL1Hook is AbstractMessageIdAuthHook {
+    using StandardHookMetadata for bytes;
+
+    // ============ Constants ============
+
+    // precompile contract on L2 for sending messages to L1
+    ArbSys public immutable arbSys;
+    // Immutable quote amount
+    uint256 public immutable GAS_QUOTE;
+
+    // ============ Constructor ============
+
+    constructor(
+        address _mailbox,
+        uint32 _destinationDomain,
+        bytes32 _ism,
+        address _arbSys,
+        uint256 _gasQuote
+    ) AbstractMessageIdAuthHook(_mailbox, _destinationDomain, _ism) {
+        arbSys = ArbSys(_arbSys);
+        GAS_QUOTE = _gasQuote;
+    }
+
+    function hookType() external pure override returns (uint8) {
+        return uint8(IPostDispatchHook.Types.ARB_L2_TO_L1);
+    }
+
+    function _quoteDispatch(
+        bytes calldata,
+        bytes calldata
+    ) internal view override returns (uint256) {
+        return GAS_QUOTE;
+    }
+
+    // ============ Internal functions ============
+
+    /// @inheritdoc AbstractMessageIdAuthHook
+    function _sendMessageId(
+        bytes calldata metadata,
+        bytes memory payload
+    ) internal override {
+        arbSys.sendTxToL1{value: metadata.msgValue(0)}(
+            TypeCasts.bytes32ToAddress(ism),
+            payload
+        );
+    }
+}
diff --git a/solidity/contracts/hooks/libs/AbstractMessageIdAuthHook.sol b/solidity/contracts/hooks/libs/AbstractMessageIdAuthHook.sol
index cd0f665838..a9e3a41e94 100644
--- a/solidity/contracts/hooks/libs/AbstractMessageIdAuthHook.sol
+++ b/solidity/contracts/hooks/libs/AbstractMessageIdAuthHook.sol
@@ -58,7 +58,7 @@ abstract contract AbstractMessageIdAuthHook is
     }
 
     /// @inheritdoc IPostDispatchHook
-    function hookType() external pure returns (uint8) {
+    function hookType() external pure virtual returns (uint8) {
         return uint8(IPostDispatchHook.Types.ID_AUTH_ISM);
     }
 
diff --git a/solidity/contracts/hooks/warp-route/RateLimitedHook.sol b/solidity/contracts/hooks/warp-route/RateLimitedHook.sol
index 0937f841be..dd46577502 100644
--- a/solidity/contracts/hooks/warp-route/RateLimitedHook.sol
+++ b/solidity/contracts/hooks/warp-route/RateLimitedHook.sol
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: MIT
 pragma solidity >=0.8.0;
+
 import {MailboxClient} from "contracts/client/MailboxClient.sol";
 import {IPostDispatchHook} from "contracts/interfaces/hooks/IPostDispatchHook.sol";
 import {Message} from "contracts/libs/Message.sol";
@@ -26,7 +27,7 @@ contract RateLimitedHook is IPostDispatchHook, MailboxClient, RateLimited {
 
     /// @inheritdoc IPostDispatchHook
     function hookType() external pure returns (uint8) {
-        return uint8(IPostDispatchHook.Types.Rate_Limited_Hook);
+        return uint8(IPostDispatchHook.Types.RATE_LIMITED);
     }
 
     /// @inheritdoc IPostDispatchHook
diff --git a/solidity/contracts/interfaces/IInterchainSecurityModule.sol b/solidity/contracts/interfaces/IInterchainSecurityModule.sol
index d4e6c30c61..d98327e745 100644
--- a/solidity/contracts/interfaces/IInterchainSecurityModule.sol
+++ b/solidity/contracts/interfaces/IInterchainSecurityModule.sol
@@ -10,7 +10,8 @@ interface IInterchainSecurityModule {
         MERKLE_ROOT_MULTISIG,
         MESSAGE_ID_MULTISIG,
         NULL, // used with relayer carrying no metadata
-        CCIP_READ
+        CCIP_READ,
+        ARB_L2_TO_L1
     }
 
     /**
diff --git a/solidity/contracts/interfaces/hooks/IPostDispatchHook.sol b/solidity/contracts/interfaces/hooks/IPostDispatchHook.sol
index 0efa08ab39..a74951b344 100644
--- a/solidity/contracts/interfaces/hooks/IPostDispatchHook.sol
+++ b/solidity/contracts/interfaces/hooks/IPostDispatchHook.sol
@@ -25,7 +25,8 @@ interface IPostDispatchHook {
         PAUSABLE,
         PROTOCOL_FEE,
         LAYER_ZERO_V1,
-        Rate_Limited_Hook
+        RATE_LIMITED,
+        ARB_L2_TO_L1
     }
 
     /**
diff --git a/solidity/contracts/isms/hook/AbstractMessageIdAuthorizedIsm.sol b/solidity/contracts/isms/hook/AbstractMessageIdAuthorizedIsm.sol
index 4aa0b9bc92..a8b8baee6c 100644
--- a/solidity/contracts/isms/hook/AbstractMessageIdAuthorizedIsm.sol
+++ b/solidity/contracts/isms/hook/AbstractMessageIdAuthorizedIsm.sol
@@ -72,26 +72,41 @@ abstract contract AbstractMessageIdAuthorizedIsm is
      */
     function verify(
         bytes calldata,
-        /*_metadata*/
+        /*metadata*/
         bytes calldata message
-    ) external returns (bool) {
-        bytes32 messageId = message.id();
+    ) external virtual returns (bool) {
+        bool verified = isVerified(message);
+        if (verified) {
+            releaseValueToRecipient(message);
+        }
+        return verified;
+    }
 
-        // check for the first bit (used for verification)
-        bool verified = verifiedMessages[messageId].isBitSet(
+    // ============ Public Functions ============
+
+    /**
+     * @notice Release the value to the recipient if the message is verified.
+     * @param message Message to release value for.
+     */
+    function releaseValueToRecipient(bytes calldata message) public {
+        bytes32 messageId = message.id();
+        uint256 _msgValue = verifiedMessages[messageId].clearBit(
             VERIFIED_MASK_INDEX
         );
-        // rest 255 bits contains the msg.value passed from the hook
-        if (verified) {
-            uint256 _msgValue = verifiedMessages[messageId].clearBit(
-                VERIFIED_MASK_INDEX
-            );
-            if (_msgValue > 0) {
-                verifiedMessages[messageId] -= _msgValue;
-                payable(message.recipientAddress()).sendValue(_msgValue);
-            }
+        if (_msgValue > 0) {
+            verifiedMessages[messageId] -= _msgValue;
+            payable(message.recipientAddress()).sendValue(_msgValue);
         }
-        return verified;
+    }
+
+    /**
+     * @notice Check if a message is verified through verifyMessageId first.
+     * @param message Message to check.
+     */
+    function isVerified(bytes calldata message) public view returns (bool) {
+        bytes32 messageId = message.id();
+        // check for the first bit (used for verification)
+        return verifiedMessages[messageId].isBitSet(VERIFIED_MASK_INDEX);
     }
 
     /**
@@ -113,5 +128,10 @@ abstract contract AbstractMessageIdAuthorizedIsm is
         emit ReceivedMessage(messageId);
     }
 
+    // ============ Internal Functions ============
+
+    /**
+     * @notice Check if sender is authorized to message `verifyMessageId`.
+     */
     function _isAuthorized() internal view virtual returns (bool);
 }
diff --git a/solidity/contracts/isms/hook/ArbL2ToL1Ism.sol b/solidity/contracts/isms/hook/ArbL2ToL1Ism.sol
new file mode 100644
index 0000000000..baba9e7bf6
--- /dev/null
+++ b/solidity/contracts/isms/hook/ArbL2ToL1Ism.sol
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+pragma solidity >=0.8.0;
+
+/*@@@@@@@       @@@@@@@@@
+ @@@@@@@@@       @@@@@@@@@
+  @@@@@@@@@       @@@@@@@@@
+   @@@@@@@@@       @@@@@@@@@
+    @@@@@@@@@@@@@@@@@@@@@@@@@
+     @@@@@  HYPERLANE  @@@@@@@
+    @@@@@@@@@@@@@@@@@@@@@@@@@
+   @@@@@@@@@       @@@@@@@@@
+  @@@@@@@@@       @@@@@@@@@
+ @@@@@@@@@       @@@@@@@@@
+@@@@@@@@@       @@@@@@@@*/
+
+// ============ Internal Imports ============
+
+import {IInterchainSecurityModule} from "../../interfaces/IInterchainSecurityModule.sol";
+import {TypeCasts} from "../../libs/TypeCasts.sol";
+import {Message} from "../../libs/Message.sol";
+import {AbstractMessageIdAuthorizedIsm} from "./AbstractMessageIdAuthorizedIsm.sol";
+
+// ============ External Imports ============
+
+import {IOutbox} from "@arbitrum/nitro-contracts/src/bridge/IOutbox.sol";
+import {CrossChainEnabledArbitrumL1} from "@openzeppelin/contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL1.sol";
+import {Address} from "@openzeppelin/contracts/utils/Address.sol";
+
+/**
+ * @title ArbL2ToL1Ism
+ * @notice Uses the native Arbitrum bridge to verify interchain messages from L2 to L1.
+ */
+contract ArbL2ToL1Ism is
+    CrossChainEnabledArbitrumL1,
+    AbstractMessageIdAuthorizedIsm
+{
+    using Message for bytes;
+    // ============ Constants ============
+
+    // module type for the ISM
+    uint8 public constant moduleType =
+        uint8(IInterchainSecurityModule.Types.ARB_L2_TO_L1);
+    // arbitrum nitro contract on L1 to forward verification
+    IOutbox public arbOutbox;
+
+    // ============ Constructor ============
+
+    constructor(
+        address _bridge,
+        address _outbox
+    ) CrossChainEnabledArbitrumL1(_bridge) {
+        require(
+            Address.isContract(_bridge),
+            "ArbL2ToL1Ism: invalid Arbitrum Bridge"
+        );
+        arbOutbox = IOutbox(_outbox);
+    }
+
+    // ============ External Functions ============
+
+    /// @inheritdoc IInterchainSecurityModule
+    function verify(
+        bytes calldata metadata,
+        bytes calldata message
+    ) external override returns (bool) {
+        bool verified = isVerified(message);
+        if (verified) {
+            releaseValueToRecipient(message);
+        }
+        return verified || _verifyWithOutboxCall(metadata, message);
+    }
+
+    // ============ Internal function ============
+
+    /**
+     * @notice Verify message directly using the arbOutbox.executeTransaction function.
+     * @dev This is a fallback in case the message is not verified by the stateful verify function first.
+     * @dev This function doesn't support msg.value as the ism.verify call doesn't support it either.
+     */
+    function _verifyWithOutboxCall(
+        bytes calldata metadata,
+        bytes calldata message
+    ) internal returns (bool) {
+        (
+            bytes32[] memory proof,
+            uint256 index,
+            address l2Sender,
+            address to,
+            uint256 l2Block,
+            uint256 l1Block,
+            uint256 l2Timestamp,
+            bytes memory data
+        ) = abi.decode(
+                metadata,
+                (
+                    bytes32[],
+                    uint256,
+                    address,
+                    address,
+                    uint256,
+                    uint256,
+                    uint256,
+                    bytes
+                )
+            );
+
+        // check if the sender of the l2 message is the authorized hook
+        require(
+            l2Sender == TypeCasts.bytes32ToAddress(authorizedHook),
+            "ArbL2ToL1Ism: l2Sender != authorizedHook"
+        );
+        // this data is an abi encoded call of verifyMessageId(bytes32 messageId)
+        require(data.length == 36, "ArbL2ToL1Ism: invalid data length");
+        bytes32 messageId = message.id();
+        bytes32 convertedBytes;
+        assembly {
+            // data = 0x[4 bytes function signature][32 bytes messageId]
+            convertedBytes := mload(add(data, 36))
+        }
+        // check if the parsed message id matches the message id of the message
+        require(
+            convertedBytes == messageId,
+            "ArbL2ToL1Ism: invalid message id"
+        );
+
+        // value send to 0
+        arbOutbox.executeTransaction(
+            proof,
+            index,
+            l2Sender,
+            to,
+            l2Block,
+            l1Block,
+            l2Timestamp,
+            0,
+            data
+        );
+        // the above bridge call will revert if the verifyMessageId call fails
+        return true;
+    }
+
+    /// @inheritdoc AbstractMessageIdAuthorizedIsm
+    function _isAuthorized() internal view override returns (bool) {
+        return
+            _crossChainSender() == TypeCasts.bytes32ToAddress(authorizedHook);
+    }
+}
diff --git a/solidity/contracts/test/TestRecipient.sol b/solidity/contracts/test/TestRecipient.sol
index 3b3b3e3afb..1d4020dd6f 100644
--- a/solidity/contracts/test/TestRecipient.sol
+++ b/solidity/contracts/test/TestRecipient.sol
@@ -46,4 +46,6 @@ contract TestRecipient is
     function setInterchainSecurityModule(address _ism) external onlyOwner {
         interchainSecurityModule = IInterchainSecurityModule(_ism);
     }
+
+    receive() external payable {}
 }
diff --git a/solidity/package.json b/solidity/package.json
index 347dcc6631..cdbe62fb88 100644
--- a/solidity/package.json
+++ b/solidity/package.json
@@ -3,6 +3,7 @@
   "description": "Core solidity contracts for Hyperlane",
   "version": "4.0.0",
   "dependencies": {
+    "@arbitrum/nitro-contracts": "^1.2.1",
     "@eth-optimism/contracts": "^0.6.0",
     "@hyperlane-xyz/utils": "4.0.0",
     "@layerzerolabs/lz-evm-oapp-v2": "2.0.2",
diff --git a/solidity/remappings.txt b/solidity/remappings.txt
index e85474338a..49ae22c339 100644
--- a/solidity/remappings.txt
+++ b/solidity/remappings.txt
@@ -1,6 +1,7 @@
-@openzeppelin=../node_modules/@openzeppelin
-@layerzerolabs=../node_modules/@layerzerolabs
+@arbitrum=../node_modules/@arbitrum
 @eth-optimism=../node_modules/@eth-optimism
+@layerzerolabs=../node_modules/@layerzerolabs
+@openzeppelin=../node_modules/@openzeppelin
 ds-test/=lib/forge-std/lib/ds-test/src/
 forge-std/=lib/forge-std/src/
-fx-portal/=lib/fx-portal/
\ No newline at end of file
+fx-portal/=lib/fx-portal/
diff --git a/solidity/script/DeployArbHook.s.sol b/solidity/script/DeployArbHook.s.sol
new file mode 100644
index 0000000000..ad9f42d77a
--- /dev/null
+++ b/solidity/script/DeployArbHook.s.sol
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+pragma solidity >=0.8.0;
+
+import "forge-std/Script.sol";
+
+import {Mailbox} from "../../contracts/Mailbox.sol";
+import {TypeCasts} from "../../contracts/libs/TypeCasts.sol";
+import {ArbL2ToL1Hook} from "../../contracts/hooks/ArbL2ToL1Hook.sol";
+import {ArbL2ToL1Ism} from "../../contracts/isms/hook/ArbL2ToL1Ism.sol";
+import {TestRecipient} from "../../contracts/test/TestRecipient.sol";
+import {TestIsm} from "../../contracts/test/TestIsm.sol";
+
+contract DeployArbHook is Script {
+    uint256 deployerPrivateKey;
+
+    ArbL2ToL1Hook hook;
+    ArbL2ToL1Ism ism;
+
+    uint32 constant L1_DOMAIN = 11155111;
+    address constant L1_MAILBOX = 0xfFAEF09B3cd11D9b20d1a19bECca54EEC2884766;
+    address constant L1_BRIDGE = 0x38f918D0E9F1b721EDaA41302E399fa1B79333a9;
+    address constant L1_OUTBOX = 0x65f07C7D521164a4d5DaC6eB8Fac8DA067A3B78F;
+    address constant L1_ISM = 0x096A1c034c7Ad113B6dB786b7BA852cB67025458; // placeholder
+    bytes32 TEST_RECIPIENT =
+        0x000000000000000000000000155b1cd2f7cbc58d403b9be341fab6cd77425175; // placeholder
+
+    address constant ARBSYS = 0x0000000000000000000000000000000000000064;
+    address constant L2_MAILBOX = 0x598facE78a4302f11E3de0bee1894Da0b2Cb71F8;
+    address constant L2_HOOK = 0xd9d99AC1C645563576b8Df22cBebFC23FB60Ec73; // placeholder
+
+    function deployIsm() external {
+        deployerPrivateKey = vm.envUint("DEPLOYER_PRIVATE_KEY");
+
+        vm.startBroadcast(deployerPrivateKey);
+
+        ism = new ArbL2ToL1Ism(L1_BRIDGE, L1_OUTBOX);
+
+        TestRecipient testRecipient = new TestRecipient();
+        testRecipient.setInterchainSecurityModule(address(ism));
+
+        vm.stopBroadcast();
+    }
+
+    function deployHook() external {
+        deployerPrivateKey = vm.envUint("DEPLOYER_PRIVATE_KEY");
+
+        vm.startBroadcast(deployerPrivateKey);
+
+        hook = new ArbL2ToL1Hook(
+            L2_MAILBOX,
+            L1_DOMAIN,
+            TypeCasts.addressToBytes32(L1_ISM),
+            ARBSYS,
+            200_000 // estimated gas amount used for verify
+        );
+
+        vm.stopBroadcast();
+    }
+
+    function deployTestRecipient() external {
+        deployerPrivateKey = vm.envUint("DEPLOYER_PRIVATE_KEY");
+
+        vm.startBroadcast(deployerPrivateKey);
+
+        TestIsm noopIsm = new TestIsm();
+        noopIsm.setVerify(true);
+        TestRecipient testRecipient = new TestRecipient();
+        testRecipient.setInterchainSecurityModule(address(noopIsm));
+
+        console.log("TestRecipient address: %s", address(testRecipient));
+
+        vm.stopBroadcast();
+    }
+
+    function setAuthorizedHook() external {
+        deployerPrivateKey = vm.envUint("DEPLOYER_PRIVATE_KEY");
+
+        vm.startBroadcast(deployerPrivateKey);
+
+        ism = ArbL2ToL1Ism(L1_ISM);
+        ism.setAuthorizedHook(TypeCasts.addressToBytes32(L2_HOOK));
+
+        vm.stopBroadcast();
+    }
+}
diff --git a/solidity/test/isms/ArbL2ToL1Ism.t.sol b/solidity/test/isms/ArbL2ToL1Ism.t.sol
new file mode 100644
index 0000000000..40d77bff6b
--- /dev/null
+++ b/solidity/test/isms/ArbL2ToL1Ism.t.sol
@@ -0,0 +1,364 @@
+// SPDX-License-Identifier: MIT or Apache-2.0
+pragma solidity ^0.8.13;
+
+import {Test} from "forge-std/Test.sol";
+
+import {TypeCasts} from "../../contracts/libs/TypeCasts.sol";
+import {MessageUtils} from "./IsmTestUtils.sol";
+import {TestMailbox} from "../../contracts/test/TestMailbox.sol";
+import {StandardHookMetadata} from "../../contracts/hooks/libs/StandardHookMetadata.sol";
+import {Message} from "../../contracts/libs/Message.sol";
+import {AbstractMessageIdAuthorizedIsm} from "../../contracts/isms/hook/AbstractMessageIdAuthorizedIsm.sol";
+import {ArbL2ToL1Hook} from "../../contracts/hooks/ArbL2ToL1Hook.sol";
+import {ArbL2ToL1Ism} from "../../contracts/isms/hook/ArbL2ToL1Ism.sol";
+import {TestRecipient} from "../../contracts/test/TestRecipient.sol";
+
+contract MockArbBridge {
+    error BridgeCallFailed();
+
+    address public activeOutbox;
+    address public l2ToL1Sender;
+
+    constructor() {
+        activeOutbox = address(this);
+    }
+
+    function setL2ToL1Sender(address _sender) external {
+        l2ToL1Sender = _sender;
+    }
+
+    function executeTransaction(
+        bytes32[] calldata /*proof*/,
+        uint256 /*index*/,
+        address /*l2Sender*/,
+        address to,
+        uint256 /*l2Block*/,
+        uint256 /*l1Block*/,
+        uint256 /*timestamp*/,
+        uint256 value,
+        bytes calldata data
+    ) external payable {
+        (bool success, bytes memory returndata) = to.call{value: value}(data);
+        if (!success) {
+            if (returndata.length > 0) {
+                // solhint-disable-next-line no-inline-assembly
+                assembly {
+                    let returndata_size := mload(returndata)
+                    revert(add(32, returndata), returndata_size)
+                }
+            } else {
+                revert BridgeCallFailed();
+            }
+        }
+    }
+}
+
+contract MockArbSys {
+    function sendTxToL1(
+        address destination,
+        bytes calldata data
+    ) external payable returns (uint256) {}
+}
+
+contract ArbL2ToL1IsmTest is Test {
+    uint8 internal constant HYPERLANE_VERSION = 1;
+    uint32 internal constant MAINNET_DOMAIN = 1;
+    uint32 internal constant ARBITRUM_DOMAIN = 42161;
+    uint256 internal constant GAS_QUOTE = 120_000;
+
+    uint256 internal constant MOCK_LEAF_INDEX = 40160;
+    uint256 internal constant MOCK_L2_BLOCK = 54220000;
+    uint256 internal constant MOCK_L1_BLOCK = 6098300;
+
+    address internal constant L2_ARBSYS_ADDRESS =
+        0x0000000000000000000000000000000000000064;
+
+    MockArbBridge internal arbBridge;
+    TestMailbox public l2Mailbox;
+    ArbL2ToL1Hook public hook;
+    ArbL2ToL1Ism public ism;
+
+    TestRecipient internal testRecipient;
+    bytes internal testMessage =
+        abi.encodePacked("Hello from the other chain!");
+    bytes internal encodedMessage;
+    bytes internal testMetadata =
+        StandardHookMetadata.overrideRefundAddress(address(this));
+    bytes32 internal messageId;
+
+    function setUp() public {
+        // Arbitrum bridge mock setup
+        vm.etch(L2_ARBSYS_ADDRESS, address(new MockArbSys()).code);
+
+        testRecipient = new TestRecipient();
+
+        encodedMessage = _encodeTestMessage();
+        messageId = Message.id(encodedMessage);
+    }
+
+    ///////////////////////////////////////////////////////////////////
+    ///                            SETUP                            ///
+    ///////////////////////////////////////////////////////////////////
+
+    function deployHook() public {
+        l2Mailbox = new TestMailbox(ARBITRUM_DOMAIN);
+        hook = new ArbL2ToL1Hook(
+            address(l2Mailbox),
+            MAINNET_DOMAIN,
+            TypeCasts.addressToBytes32(address(ism)),
+            L2_ARBSYS_ADDRESS,
+            GAS_QUOTE
+        );
+    }
+
+    function deployIsm() public {
+        arbBridge = new MockArbBridge();
+
+        ism = new ArbL2ToL1Ism(address(arbBridge), address(arbBridge));
+    }
+
+    function deployAll() public {
+        deployIsm();
+        deployHook();
+
+        ism.setAuthorizedHook(TypeCasts.addressToBytes32(address(hook)));
+    }
+
+    function test_postDispatch() public {
+        deployAll();
+
+        bytes memory encodedHookData = abi.encodeCall(
+            AbstractMessageIdAuthorizedIsm.verifyMessageId,
+            (messageId)
+        );
+
+        l2Mailbox.updateLatestDispatchedId(messageId);
+
+        vm.expectCall(
+            L2_ARBSYS_ADDRESS,
+            abi.encodeCall(
+                MockArbSys.sendTxToL1,
+                (address(ism), encodedHookData)
+            )
+        );
+        hook.postDispatch(testMetadata, encodedMessage);
+    }
+
+    function testFork_postDispatch_revertWhen_chainIDNotSupported() public {
+        deployAll();
+
+        bytes memory message = MessageUtils.formatMessage(
+            0,
+            uint32(0),
+            ARBITRUM_DOMAIN,
+            TypeCasts.addressToBytes32(address(this)),
+            2, // wrong domain
+            TypeCasts.addressToBytes32(address(testRecipient)),
+            testMessage
+        );
+
+        l2Mailbox.updateLatestDispatchedId(Message.id(message));
+        vm.expectRevert(
+            "AbstractMessageIdAuthHook: invalid destination domain"
+        );
+        hook.postDispatch(testMetadata, message);
+    }
+
+    function test_postDispatch_revertWhen_notLastDispatchedMessage() public {
+        deployAll();
+
+        // vm.expectRevert(
+        //     "AbstractMessageIdAuthHook: message not latest dispatched"
+        // );
+        // hook.postDispatch(testMetadata, encodedMessage);
+    }
+
+    function test_verify_outboxCall() public {
+        deployAll();
+
+        bytes memory encodedOutboxTxMetadata = _encodeOutboxTx(
+            address(hook),
+            address(ism),
+            messageId
+        );
+
+        arbBridge.setL2ToL1Sender(address(hook));
+        assertTrue(ism.verify(encodedOutboxTxMetadata, encodedMessage));
+    }
+
+    function test_verify_statefulVerify() public {
+        deployAll();
+
+        bytes memory encodedHookData = abi.encodeCall(
+            AbstractMessageIdAuthorizedIsm.verifyMessageId,
+            (messageId)
+        );
+
+        arbBridge.setL2ToL1Sender(address(hook));
+        arbBridge.executeTransaction{value: 1 ether}(
+            new bytes32[](0),
+            MOCK_LEAF_INDEX,
+            address(hook),
+            address(ism),
+            MOCK_L2_BLOCK,
+            MOCK_L1_BLOCK,
+            block.timestamp,
+            1 ether,
+            encodedHookData
+        );
+
+        vm.etch(address(arbBridge), new bytes(0)); // this is a way to test that the arbBridge isn't called again
+        assertTrue(ism.verify(new bytes(0), encodedMessage));
+        assertEq(address(testRecipient).balance, 1 ether);
+    }
+
+    function test_verify_statefulAndOutbox() public {
+        deployAll();
+
+        bytes memory encodedHookData = abi.encodeCall(
+            AbstractMessageIdAuthorizedIsm.verifyMessageId,
+            (messageId)
+        );
+
+        arbBridge.setL2ToL1Sender(address(hook));
+        arbBridge.executeTransaction{value: 1 ether}(
+            new bytes32[](0),
+            MOCK_LEAF_INDEX,
+            address(hook),
+            address(ism),
+            MOCK_L2_BLOCK,
+            MOCK_L1_BLOCK,
+            block.timestamp,
+            1 ether,
+            encodedHookData
+        );
+
+        bytes memory encodedOutboxTxMetadata = _encodeOutboxTx(
+            address(hook),
+            address(ism),
+            messageId
+        );
+
+        vm.etch(address(arbBridge), new bytes(0)); // this is a way to test that the arbBridge isn't called again
+        assertTrue(ism.verify(encodedOutboxTxMetadata, encodedMessage));
+        assertEq(address(testRecipient).balance, 1 ether);
+    }
+
+    function test_verify_revertsWhen_noStatefulOrOutbox() public {
+        deployAll();
+
+        vm.expectRevert();
+        ism.verify(new bytes(0), encodedMessage);
+    }
+
+    function test_verify_revertsWhen_notAuthorizedHook() public {
+        deployAll();
+
+        bytes memory encodedOutboxTxMetadata = _encodeOutboxTx(
+            address(this),
+            address(ism),
+            messageId
+        );
+
+        arbBridge.setL2ToL1Sender(address(hook));
+
+        vm.expectRevert("ArbL2ToL1Ism: l2Sender != authorizedHook");
+        ism.verify(encodedOutboxTxMetadata, encodedMessage);
+    }
+
+    function test_verify_revertsWhen_invalidIsm() public {
+        deployAll();
+
+        bytes memory encodedOutboxTxMetadata = _encodeOutboxTx(
+            address(hook),
+            address(this),
+            messageId
+        );
+
+        arbBridge.setL2ToL1Sender(address(hook));
+
+        vm.expectRevert(); // BridgeCallFailed()
+        ism.verify(encodedOutboxTxMetadata, encodedMessage);
+    }
+
+    function test_verify_revertsWhen_incorrectMessageId() public {
+        deployAll();
+
+        bytes32 incorrectMessageId = keccak256("incorrect message id");
+
+        bytes memory encodedOutboxTxMetadata = _encodeOutboxTx(
+            address(hook),
+            address(ism),
+            incorrectMessageId
+        );
+
+        bytes memory encodedHookData = abi.encodeCall(
+            AbstractMessageIdAuthorizedIsm.verifyMessageId,
+            (incorrectMessageId)
+        );
+
+        arbBridge.setL2ToL1Sender(address(hook));
+
+        // through outbox call
+        vm.expectRevert("ArbL2ToL1Ism: invalid message id");
+        ism.verify(encodedOutboxTxMetadata, encodedMessage);
+
+        // through statefulVerify
+        arbBridge.executeTransaction(
+            new bytes32[](0),
+            MOCK_LEAF_INDEX,
+            address(hook),
+            address(ism),
+            MOCK_L2_BLOCK,
+            MOCK_L1_BLOCK,
+            block.timestamp,
+            0,
+            encodedHookData
+        );
+
+        vm.etch(address(arbBridge), new bytes(0)); // to stop the outbox route
+        vm.expectRevert();
+        assertFalse(ism.verify(new bytes(0), encodedMessage));
+    }
+
+    // function test_verify_withMsgValue
+
+    /* ============ helper functions ============ */
+
+    function _encodeOutboxTx(
+        address _hook,
+        address _ism,
+        bytes32 _messageId
+    ) internal view returns (bytes memory) {
+        bytes memory encodedHookData = abi.encodeCall(
+            AbstractMessageIdAuthorizedIsm.verifyMessageId,
+            (_messageId)
+        );
+
+        bytes32[] memory proof = new bytes32[](16);
+        return
+            abi.encode(
+                proof,
+                MOCK_LEAF_INDEX,
+                _hook,
+                _ism,
+                MOCK_L2_BLOCK,
+                MOCK_L1_BLOCK,
+                block.timestamp,
+                encodedHookData
+            );
+    }
+
+    function _encodeTestMessage() internal view returns (bytes memory) {
+        return
+            MessageUtils.formatMessage(
+                HYPERLANE_VERSION,
+                uint32(0),
+                ARBITRUM_DOMAIN,
+                TypeCasts.addressToBytes32(address(this)),
+                MAINNET_DOMAIN,
+                TypeCasts.addressToBytes32(address(testRecipient)),
+                testMessage
+            );
+    }
+}
diff --git a/yarn.lock b/yarn.lock
index 80adf046c8..1ac6d807b6 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -29,6 +29,18 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@arbitrum/nitro-contracts@npm:^1.2.1":
+  version: 1.2.1
+  resolution: "@arbitrum/nitro-contracts@npm:1.2.1"
+  dependencies:
+    "@offchainlabs/upgrade-executor": "npm:1.1.0-beta.0"
+    "@openzeppelin/contracts": "npm:4.5.0"
+    "@openzeppelin/contracts-upgradeable": "npm:4.5.2"
+    patch-package: "npm:^6.4.7"
+  checksum: b8e682e85a6cb45757427d8d24a59752e4e69167d8347ddf36bb299a64a892d9d847bd11ee8d4c6b61b62688e83657b3a1691a1d1dfb924006b39caa64ec2df1
+  languageName: node
+  linkType: hard
+
 "@arbitrum/sdk@npm:^3.0.0":
   version: 3.0.0
   resolution: "@arbitrum/sdk@npm:3.0.0"
@@ -5734,6 +5746,7 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "@hyperlane-xyz/core@workspace:solidity"
   dependencies:
+    "@arbitrum/nitro-contracts": "npm:^1.2.1"
     "@eth-optimism/contracts": "npm:^0.6.0"
     "@hyperlane-xyz/utils": "npm:4.0.0"
     "@layerzerolabs/lz-evm-oapp-v2": "npm:2.0.2"
@@ -7554,6 +7567,16 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@offchainlabs/upgrade-executor@npm:1.1.0-beta.0":
+  version: 1.1.0-beta.0
+  resolution: "@offchainlabs/upgrade-executor@npm:1.1.0-beta.0"
+  dependencies:
+    "@openzeppelin/contracts": "npm:4.7.3"
+    "@openzeppelin/contracts-upgradeable": "npm:4.7.3"
+  checksum: a8cd0cc24103cc42021c452220005efde535ba3596ec2ba5eb6dc299d1f3291c38a3d859621d7983bd7c43c80606d6e7d906e1081a1e499455ddea7ba64ab355
+  languageName: node
+  linkType: hard
+
 "@openzeppelin-3/contracts@npm:@openzeppelin/contracts@^3.4.2-solc-0.7":
   version: 3.4.2
   resolution: "@openzeppelin/contracts@npm:3.4.2"
@@ -7568,6 +7591,20 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@openzeppelin/contracts-upgradeable@npm:4.5.2":
+  version: 4.5.2
+  resolution: "@openzeppelin/contracts-upgradeable@npm:4.5.2"
+  checksum: 5e246da7a44bb982a312ebf79978735712140692d46273566e490159b98b9041ca72cc08c3d05172137a389be4caad5afc001480bc5557f3d47162f4626e3723
+  languageName: node
+  linkType: hard
+
+"@openzeppelin/contracts-upgradeable@npm:4.7.3":
+  version: 4.7.3
+  resolution: "@openzeppelin/contracts-upgradeable@npm:4.7.3"
+  checksum: 7c72ffeca867478b5aa8e8c7adb3d1ce114cfdc797ed4f3cd074788cf4da25d620ffffd624ac7e9d1223eecffeea9f7b79200ff70dc464cc828c470ccd12ddf1
+  languageName: node
+  linkType: hard
+
 "@openzeppelin/contracts-upgradeable@npm:^4.6.0":
   version: 4.9.5
   resolution: "@openzeppelin/contracts-upgradeable@npm:4.9.5"
@@ -7589,6 +7626,20 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@openzeppelin/contracts@npm:4.5.0":
+  version: 4.5.0
+  resolution: "@openzeppelin/contracts@npm:4.5.0"
+  checksum: 8bfa1733732420331728cedd7f1f5f4e4ae0700b32c9e5def19b2d42dbb0b246709e8e22abd457e8269d743012ff2aed4e3f100a942f45d9507cb78d5dbd435b
+  languageName: node
+  linkType: hard
+
+"@openzeppelin/contracts@npm:4.7.3":
+  version: 4.7.3
+  resolution: "@openzeppelin/contracts@npm:4.7.3"
+  checksum: 3d16ed8943938373ecc331c2ab83c3e8d0d89aed0c2a109aaa61ca6524b4c31cb5a81185c6f93ce9ee2dda685a4328fd85bd217929ae598f4be813d5d4cd1b78
+  languageName: node
+  linkType: hard
+
 "@openzeppelin/contracts@npm:^4.2.0":
   version: 4.9.6
   resolution: "@openzeppelin/contracts@npm:4.9.6"
@@ -10752,6 +10803,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@yarnpkg/lockfile@npm:^1.1.0":
+  version: 1.1.0
+  resolution: "@yarnpkg/lockfile@npm:1.1.0"
+  checksum: cd19e1114aaf10a05126aeea8833ef4ca8af8a46e88e12884f8359d19333fd19711036dbc2698dbe937f81f037070cf9a8da45c2e8c6ca19cafd7d15659094ed
+  languageName: node
+  linkType: hard
+
 "JSONStream@npm:^1.3.5":
   version: 1.3.5
   resolution: "JSONStream@npm:1.3.5"
@@ -13154,6 +13212,19 @@ __metadata:
   languageName: node
   linkType: hard
 
+"cross-spawn@npm:^6.0.5":
+  version: 6.0.5
+  resolution: "cross-spawn@npm:6.0.5"
+  dependencies:
+    nice-try: "npm:^1.0.4"
+    path-key: "npm:^2.0.1"
+    semver: "npm:^5.5.0"
+    shebang-command: "npm:^1.2.0"
+    which: "npm:^1.2.9"
+  checksum: f07e643b4875f26adffcd7f13bc68d9dff20cf395f8ed6f43a23f3ee24fc3a80a870a32b246fd074e514c8fd7da5f978ac6a7668346eec57aa87bac89c1ed3a1
+  languageName: node
+  linkType: hard
+
 "cross-spawn@npm:^7.0.2, cross-spawn@npm:^7.0.3":
   version: 7.0.3
   resolution: "cross-spawn@npm:7.0.3"
@@ -15211,6 +15282,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"find-yarn-workspace-root@npm:^2.0.0":
+  version: 2.0.0
+  resolution: "find-yarn-workspace-root@npm:2.0.0"
+  dependencies:
+    micromatch: "npm:^4.0.2"
+  checksum: 7fa7942849eef4d5385ee96a0a9a5a9afe885836fd72ed6a4280312a38690afea275e7d09b343fe97daf0412d833f8ac4b78c17fc756386d9ebebf0759d707a7
+  languageName: node
+  linkType: hard
+
 "flat-cache@npm:^3.0.4":
   version: 3.0.4
   resolution: "flat-cache@npm:3.0.4"
@@ -15446,7 +15526,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"fs-extra@npm:^9.1.0":
+"fs-extra@npm:^9.0.0, fs-extra@npm:^9.1.0":
   version: 9.1.0
   resolution: "fs-extra@npm:9.1.0"
   dependencies:
@@ -16181,7 +16261,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"graceful-fs@npm:^4.1.5, graceful-fs@npm:^4.2.4, graceful-fs@npm:^4.2.9":
+"graceful-fs@npm:^4.1.11, graceful-fs@npm:^4.1.5, graceful-fs@npm:^4.2.4, graceful-fs@npm:^4.2.9":
   version: 4.2.11
   resolution: "graceful-fs@npm:4.2.11"
   checksum: bf152d0ed1dc159239db1ba1f74fdbc40cb02f626770dcd5815c427ce0688c2635a06ed69af364396da4636d0408fcf7d4afdf7881724c3307e46aff30ca49e2
@@ -17182,6 +17262,17 @@ __metadata:
   languageName: node
   linkType: hard
 
+"is-ci@npm:^2.0.0":
+  version: 2.0.0
+  resolution: "is-ci@npm:2.0.0"
+  dependencies:
+    ci-info: "npm:^2.0.0"
+  bin:
+    is-ci: bin.js
+  checksum: 77b869057510f3efa439bbb36e9be429d53b3f51abd4776eeea79ab3b221337fe1753d1e50058a9e2c650d38246108beffb15ccfd443929d77748d8c0cc90144
+  languageName: node
+  linkType: hard
+
 "is-ci@npm:^3.0.1":
   version: 3.0.1
   resolution: "is-ci@npm:3.0.1"
@@ -17220,6 +17311,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"is-docker@npm:^2.0.0":
+  version: 2.2.1
+  resolution: "is-docker@npm:2.2.1"
+  bin:
+    is-docker: cli.js
+  checksum: 3fef7ddbf0be25958e8991ad941901bf5922ab2753c46980b60b05c1bf9c9c2402d35e6dc32e4380b980ef5e1970a5d9d5e5aa2e02d77727c3b6b5e918474c56
+  languageName: node
+  linkType: hard
+
 "is-docker@npm:^3.0.0":
   version: 3.0.0
   resolution: "is-docker@npm:3.0.0"
@@ -17507,6 +17607,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"is-wsl@npm:^2.1.1":
+  version: 2.2.0
+  resolution: "is-wsl@npm:2.2.0"
+  dependencies:
+    is-docker: "npm:^2.0.0"
+  checksum: 20849846ae414997d290b75e16868e5261e86ff5047f104027026fd61d8b5a9b0b3ade16239f35e1a067b3c7cc02f70183cb661010ed16f4b6c7c93dad1b19d8
+  languageName: node
+  linkType: hard
+
 "is-wsl@npm:^3.1.0":
   version: 3.1.0
   resolution: "is-wsl@npm:3.1.0"
@@ -18494,6 +18603,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"klaw-sync@npm:^6.0.0":
+  version: 6.0.0
+  resolution: "klaw-sync@npm:6.0.0"
+  dependencies:
+    graceful-fs: "npm:^4.1.11"
+  checksum: 0da397f8961313c3ef8f79fb63af9002cde5a8fb2aeb1a37351feff0dd6006129c790400c3f5c3b4e757bedcabb13d21ec0a5eaef5a593d59515d4f2c291e475
+  languageName: node
+  linkType: hard
+
 "klaw@npm:^1.0.0":
   version: 1.3.1
   resolution: "klaw@npm:1.3.1"
@@ -20113,6 +20231,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"nice-try@npm:^1.0.4":
+  version: 1.0.5
+  resolution: "nice-try@npm:1.0.5"
+  checksum: 0b4af3b5bb5d86c289f7a026303d192a7eb4417231fe47245c460baeabae7277bcd8fd9c728fb6bd62c30b3e15cd6620373e2cf33353b095d8b403d3e8a15aff
+  languageName: node
+  linkType: hard
+
 "nise@npm:^5.1.1":
   version: 5.1.1
   resolution: "nise@npm:5.1.1"
@@ -20680,6 +20805,16 @@ __metadata:
   languageName: node
   linkType: hard
 
+"open@npm:^7.4.2":
+  version: 7.4.2
+  resolution: "open@npm:7.4.2"
+  dependencies:
+    is-docker: "npm:^2.0.0"
+    is-wsl: "npm:^2.1.1"
+  checksum: 4fc02ed3368dcd5d7247ad3566433ea2695b0713b041ebc0eeb2f0f9e5d4e29fc2068f5cdd500976b3464e77fe8b61662b1b059c73233ccc601fe8b16d6c1cd6
+  languageName: node
+  linkType: hard
+
 "optionator@npm:^0.8.1":
   version: 0.8.3
   resolution: "optionator@npm:0.8.3"
@@ -20934,6 +21069,30 @@ __metadata:
   languageName: node
   linkType: hard
 
+"patch-package@npm:^6.4.7":
+  version: 6.5.1
+  resolution: "patch-package@npm:6.5.1"
+  dependencies:
+    "@yarnpkg/lockfile": "npm:^1.1.0"
+    chalk: "npm:^4.1.2"
+    cross-spawn: "npm:^6.0.5"
+    find-yarn-workspace-root: "npm:^2.0.0"
+    fs-extra: "npm:^9.0.0"
+    is-ci: "npm:^2.0.0"
+    klaw-sync: "npm:^6.0.0"
+    minimist: "npm:^1.2.6"
+    open: "npm:^7.4.2"
+    rimraf: "npm:^2.6.3"
+    semver: "npm:^5.6.0"
+    slash: "npm:^2.0.0"
+    tmp: "npm:^0.0.33"
+    yaml: "npm:^1.10.2"
+  bin:
+    patch-package: index.js
+  checksum: e15b3848f008da2cc659abd6d84dfeab6ed25a999ba25692071c13409f198dad28b6e451ecfebc2139a0847ad8e608575d6724bcc887c56169df8a733b849e79
+  languageName: node
+  linkType: hard
+
 "path-browserify@npm:^1.0.0":
   version: 1.0.1
   resolution: "path-browserify@npm:1.0.1"
@@ -20962,6 +21121,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"path-key@npm:^2.0.1":
+  version: 2.0.1
+  resolution: "path-key@npm:2.0.1"
+  checksum: 6e654864e34386a2a8e6bf72cf664dcabb76574dd54013add770b374384d438aca95f4357bb26935b514a4e4c2c9b19e191f2200b282422a76ee038b9258c5e7
+  languageName: node
+  linkType: hard
+
 "path-key@npm:^3.0.0, path-key@npm:^3.1.0":
   version: 3.1.1
   resolution: "path-key@npm:3.1.1"
@@ -22446,7 +22612,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"rimraf@npm:^2.2.8":
+"rimraf@npm:^2.2.8, rimraf@npm:^2.6.3":
   version: 2.7.1
   resolution: "rimraf@npm:2.7.1"
   dependencies:
@@ -22693,7 +22859,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"semver@npm:2 || 3 || 4 || 5":
+"semver@npm:2 || 3 || 4 || 5, semver@npm:^5.6.0":
   version: 5.7.2
   resolution: "semver@npm:5.7.2"
   bin:
@@ -23026,6 +23192,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"slash@npm:^2.0.0":
+  version: 2.0.0
+  resolution: "slash@npm:2.0.0"
+  checksum: 512d4350735375bd11647233cb0e2f93beca6f53441015eea241fe784d8068281c3987fbaa93e7ef1c38df68d9c60013045c92837423c69115297d6169aa85e6
+  languageName: node
+  linkType: hard
+
 "slash@npm:^3.0.0":
   version: 3.0.0
   resolution: "slash@npm:3.0.0"