diff --git a/contracts/core/extensions/CoreIssuanceOrder.sol b/contracts/core/extensions/CoreIssuanceOrder.sol
index c0329b876..36f3b6404 100644
--- a/contracts/core/extensions/CoreIssuanceOrder.sol
+++ b/contracts/core/extensions/CoreIssuanceOrder.sol
@@ -45,8 +45,9 @@ contract CoreIssuanceOrder is
     /* ============ Constants ============ */
 
     uint256 constant HEADER_LENGTH = 64;
-    
+
     string constant INVALID_EXCHANGE = "Exchange does not exist.";
+    string constant INVALID_CANCEL_ORDER = "Only maker can cancel order.";
     string constant INVALID_SIGNATURE = "Invalid order signature.";
     string constant INVALID_TOKEN_AMOUNTS = "Quantity and makerTokenAmount should be greater than 0.";
     string constant ORDER_EXPIRED = "This order has expired.";
@@ -94,7 +95,7 @@ contract CoreIssuanceOrder is
             )
         });
 
-        // Verify order is valid
+        // Verify order is valid and return amount to be filled
         validateOrder(
             order,
             _fillQuantity
@@ -115,6 +116,10 @@ contract CoreIssuanceOrder is
         // Execute exchange orders
         executeExchangeOrders(_orderData);
 
+        // TO DO: When openOrder amount functionality added these must change
+        // Tally fill in orderFills mapping
+        state.orderFills[order.orderHash] = state.orderFills[order.orderHash].add(_fillQuantity);
+
         //Issue Set
         issueInternal(
             order.makerAddress,
@@ -123,6 +128,51 @@ contract CoreIssuanceOrder is
         );
     }
 
+    /**
+     * Cancel an issuance order
+     *
+     * @param  _addresses      [setAddress, makerAddress, makerToken, relayerToken]
+     * @param  _values         [quantity, makerTokenAmount, expiration, relayerTokenAmount, salt]
+     * @param  _cancelQuantity Quantity of set to be filled
+     */
+    function cancelOrder(
+        address[4] _addresses,
+        uint[5] _values,
+        uint _cancelQuantity
+    )
+        external
+        isPositiveQuantity(_cancelQuantity)
+    {
+        OrderLibrary.IssuanceOrder memory order = OrderLibrary.IssuanceOrder({
+            setAddress: _addresses[0],
+            quantity: _values[0],
+            makerAddress: _addresses[1],
+            makerToken: _addresses[2],
+            makerTokenAmount: _values[1],
+            expiration: _values[2],
+            relayerToken: _addresses[3],
+            relayerTokenAmount: _values[3],
+            salt: _values[4],
+            orderHash: OrderLibrary.generateOrderHash(
+                _addresses,
+                _values
+            )
+        });
+
+        // Make sure cancel order comes from maker
+        require(order.makerAddress == msg.sender, INVALID_CANCEL_ORDER);
+
+        // Verify order is valid and return amount to be cancelled
+        validateOrder(
+            order,
+            _cancelQuantity
+        );
+
+        // TO DO: When openOrder amount functionality added these must change
+        // Tally cancel in orderCancels mapping
+        state.orderCancels[order.orderHash] = state.orderCancels[order.orderHash].add(_cancelQuantity);
+    }
+
     /* ============ Private Functions ============ */
 
     /**
diff --git a/contracts/core/lib/CoreState.sol b/contracts/core/lib/CoreState.sol
index 2254e3a1e..6d3b4dd74 100644
--- a/contracts/core/lib/CoreState.sol
+++ b/contracts/core/lib/CoreState.sol
@@ -96,4 +96,20 @@ contract CoreState {
     {
         return state.validSets[_set];
     }
+
+    function orderFills(bytes32 _orderHash)
+        public
+        view
+        returns(uint)
+    {
+        return state.orderFills[_orderHash];
+    }
+
+    function orderCancels(bytes32 _orderHash)
+        public
+        view
+        returns(uint)
+    {
+        return state.orderCancels[_orderHash];
+    }
 }
diff --git a/test/core/extensions/coreIssuanceOrder.spec.ts b/test/core/extensions/coreIssuanceOrder.spec.ts
index 076544683..c9a31e00b 100644
--- a/test/core/extensions/coreIssuanceOrder.spec.ts
+++ b/test/core/extensions/coreIssuanceOrder.spec.ts
@@ -156,6 +156,16 @@ contract("CoreIssuanceOrder", (accounts) => {
       assertTokenBalance(setToken, existingBalance.add(subjectQuantityToIssue), signerAddress);
     });
 
+    it("marks the correct amount as filled in orderFills mapping", async () => {
+      const preFilled = await core.orderFills.callAsync(issuanceOrderParams.orderHash);
+      expect(preFilled).to.be.bignumber.equal(ZERO);
+
+      await subject();
+
+      const filled = await core.orderFills.callAsync(issuanceOrderParams.orderHash);
+      expect(filled).to.be.bignumber.equal(subjectQuantityToIssue);
+    });
+
     describe("when the quantity to issue is not positive", async () => {
       beforeEach(async () => {
         subjectQuantityToIssue = ZERO;
@@ -236,4 +246,112 @@ contract("CoreIssuanceOrder", (accounts) => {
       });
     });
   });
+
+  describe("#cancelOrder", async () => {
+    let subjectCaller: Address;
+    let subjectQuantityToCancel: BigNumber;
+    let subjectExchangeOrdersData: Bytes32;
+
+    const naturalUnit: BigNumber = ether(2);
+    let components: StandardTokenMockContract[] = [];
+    let componentUnits: BigNumber[];
+    let setToken: SetTokenContract;
+    let signerAddress: Address;
+    let componentAddresses: Address[];
+
+    let issuanceOrderParams: any;
+
+    beforeEach(async () => {
+      signerAddress = signerAccount;
+
+      components = await erc20Wrapper.deployTokensAsync(2, signerAddress); //For current purposes issue to maker/signer
+      await erc20Wrapper.approveTransfersAsync(components, transferProxy.address, signerAddress);
+
+      componentAddresses = _.map(components, (token) => token.address);
+      componentUnits = _.map(components, () => ether(4)); // Multiple of naturalUnit
+      setToken = await coreWrapper.createSetTokenAsync(
+        core,
+        setTokenFactory.address,
+        componentAddresses,
+        componentUnits,
+        naturalUnit,
+      );
+
+      await coreWrapper.registerDefaultExchanges(core);
+
+      subjectCaller = signerAccount;
+      subjectQuantityToCancel = ether(2);
+      issuanceOrderParams = await generateFillOrderParameters(setToken.address, signerAddress, signerAddress, componentAddresses[0]);
+      subjectExchangeOrdersData = generateOrdersDataForOrderCount(3);
+    });
+
+    async function subject(): Promise<string> {
+      return core.cancelOrder.sendTransactionAsync(
+        issuanceOrderParams.addresses,
+        issuanceOrderParams.values,
+        subjectQuantityToCancel,
+        { from: subjectCaller },
+      );
+    }
+
+    it("marks the correct amount as canceled in orderCancels mapping", async () => {
+      const preCanceled = await core.orderCancels.callAsync(issuanceOrderParams.orderHash);
+      expect(preCanceled).to.be.bignumber.equal(ZERO);
+
+      await subject();
+
+      const canceled = await core.orderCancels.callAsync(issuanceOrderParams.orderHash);
+      expect(canceled).to.be.bignumber.equal(subjectQuantityToCancel);
+    });
+
+    describe("when the quantity to cancel is not positive", async () => {
+      beforeEach(async () => {
+        subjectQuantityToCancel = ZERO;
+      });
+
+      it("should revert", async () => {
+        await expectRevertError(subject());
+      });
+    });
+
+    describe("when the transaction sender is not the maker", async () => {
+      beforeEach(async () => {
+        subjectCaller = takerAccount;
+      });
+
+      it("should revert", async () => {
+        await expectRevertError(subject());
+      });
+    });
+
+    describe("when the order has expired", async () => {
+      beforeEach(async () => {
+        issuanceOrderParams = await generateFillOrderParameters(setToken.address, signerAddress, signerAddress, componentAddresses[0], undefined, undefined, -1)
+      });
+
+      it("should revert", async () => {
+        await expectRevertError(subject());
+      });
+    });
+
+    describe("when invalid Set Token quantity in Issuance Order", async () => {
+      beforeEach(async () => {
+        issuanceOrderParams = await generateFillOrderParameters(setToken.address, signerAddress, signerAddress, componentAddresses[0], ZERO)
+      });
+
+      it("should revert", async () => {
+        await expectRevertError(subject());
+      });
+    });
+
+    describe("when invalid makerTokenAmount in Issuance Order", async () => {
+      beforeEach(async () => {
+        issuanceOrderParams = await generateFillOrderParameters(setToken.address, signerAddress, signerAddress, componentAddresses[0], undefined, ZERO)
+      });
+
+      it("should revert", async () => {
+        await expectRevertError(subject());
+      });
+    });
+  });
 });