diff --git a/src/Services/Catalog/Catalog.API/Model/CatalogItem.cs b/src/Services/Catalog/Catalog.API/Model/CatalogItem.cs
index 47cfa7c73..f3c04f595 100644
--- a/src/Services/Catalog/Catalog.API/Model/CatalogItem.cs
+++ b/src/Services/Catalog/Catalog.API/Model/CatalogItem.cs
@@ -1,4 +1,5 @@
-using System;
+using Catalog.API.Infrastructure.Exceptions;
+using System;
 
 namespace Microsoft.eShopOnContainers.Services.Catalog.API.Model
 {
@@ -14,8 +15,6 @@ namespace Microsoft.eShopOnContainers.Services.Catalog.API.Model
 
         public string PictureUri { get; set; }
 
-        public int Stock { get; set; }
-
         public int CatalogTypeId { get; set; }
 
         public CatalogType CatalogType { get; set; }
@@ -24,6 +23,79 @@ namespace Microsoft.eShopOnContainers.Services.Catalog.API.Model
 
         public CatalogBrand CatalogBrand { get; set; }
 
-        public CatalogItem() { }     
+        // Quantity in stock
+        public int AvailableStock { get; set; }
+
+        // Available stock at which we should reorder
+        public int RestockThreshold { get; set; }
+
+
+        // Maximum number of units that can be in-stock at any time (due to physicial/logistical constraints in warehouses)
+        public int MaxStockThreshold { get; set; }
+
+        /// <summary>
+        /// True if item is on reorder
+        /// </summary>
+        public bool OnReorder { get; set; }
+
+        public CatalogItem() { }
+
+
+        /// <summary>
+        /// Decrements the quantity of a particular item in inventory and ensures the restockThreshold hasn't
+        /// been breached. If so, a RestockRequest is generated in CheckThreshold. 
+        /// 
+        /// If there is sufficient stock of an item, then the integer returned at the end of this call should be the same as quantityDesired. 
+        /// In the event that there is not sufficient stock available, the method will remove whatever stock is available and return that quantity to the client.
+        /// In this case, it is the responsibility of the client to determine if the amount that is returned is the same as quantityDesired.
+        /// It is invalid to pass in a negative number. 
+        /// </summary>
+        /// <param name="quantityDesired"></param>
+        /// <returns>int: Returns the number actually removed from stock. </returns>
+        /// 
+        public int RemoveStock(int quantityDesired)
+        {
+            if (AvailableStock == 0)
+            {
+                throw new CatalogDomainException($"Empty stock, product item {Name} is sold out");
+            }
+
+            if (quantityDesired <= 0)
+            {
+                throw new CatalogDomainException($"Item units desired should be greater than cero");
+            }
+
+            int removed = Math.Min(quantityDesired, this.AvailableStock);
+
+            this.AvailableStock -= removed;
+
+            return removed;
+        }
+
+        /// <summary>
+        /// Increments the quantity of a particular item in inventory.
+        /// <param name="quantity"></param>
+        /// <returns>int: Returns the quantity that has been added to stock</returns>
+        /// </summary>
+        public int AddStock(int quantity)
+        {
+            int original = this.AvailableStock;
+
+            // The quantity that the client is trying to add to stock is greater than what can be physically accommodated in the Warehouse
+            if ((this.AvailableStock + quantity) > this.MaxStockThreshold)
+            {
+                // For now, this method only adds new units up maximum stock threshold. In an expanded version of this application, we
+                //could include tracking for the remaining units and store information about overstock elsewhere. 
+                this.AvailableStock += (this.MaxStockThreshold - this.AvailableStock);
+            }
+            else
+            {
+                this.AvailableStock += quantity;
+            }
+
+            this.OnReorder = false;
+
+            return this.AvailableStock - original;
+        }
     }
-}
+}
\ No newline at end of file