diff --git a/orderBook.js b/orderBook.js
new file mode 100644
index 0000000..41c0928
--- /dev/null
+++ b/orderBook.js
@@ -0,0 +1,63 @@
+
+function reconcileOrder(existingBook, incomingOrder) {
+  let updatedBook = []
+  let newOrders = []
+
+  // If the existingOrderBook is empty, add incomingOrder
+  if (!existingBook.length) {
+    let updatedBook = existingBook.concat({ ...incomingOrder })
+
+    return updatedBook
+  }
+
+  // loop through the existingBook objects
+  for (let i = 0; i < existingBook.length; i++) {
+    // set variables to simplify reading
+    const bookType = existingBook[i].type
+    const bookPrice = existingBook[i].price
+    const orderType = incomingOrder.type
+    let orderPrice = incomingOrder.price
+    let bookQuantity = existingBook[i].quantity
+    let orderQuantity = incomingOrder.quantity
+
+    // if buy and sell match (same price and quantity)
+    if (bookType !== orderType &&
+      bookPrice === orderPrice &&
+      bookQuantity === orderQuantity) {
+      // if all are true set incoming price to true
+      incomingOrder.price = true
+      // if buy and sell work, but quantities are different
+    } else if (bookType !== orderType &&
+      bookPrice === orderPrice &&
+      bookQuantity !== orderQuantity) {
+      // if existing book quantity is greater than incoming order quantity
+      if (bookQuantity > orderQuantity) {
+        //book quantity is equal to book quantity minus order quantity
+        existingBook[i].quantity -= orderQuantity
+        // set order quantity to false
+        incomingOrder.quantity = false
+        newOrders.push(existingBook[i])
+      } else {
+        //if existing book quantity is less than incoming order quantity
+        incomingOrder.quantity -= bookQuantity
+      }
+    } else {
+      // for other conditions push existingBook to the updatedBook
+      updatedBook.push(existingBook[i])
+    }
+  }
+
+  // and incoming order quantity is not 0 (also see above)
+  // if the price of the incomingOrder is not true (see above)
+  // push incoming order to updatedBook
+  if (incomingOrder.quantity !== false &&
+    incomingOrder.price !== true) {
+    updatedBook.push(incomingOrder)
+  }
+
+  return updatedBook.concat(newOrders)
+}
+
+module.exports = reconcileOrder
+
+