diff --git a/CryptoExchange.Net/Interfaces/ISymbolOrderBook.cs b/CryptoExchange.Net/Interfaces/ISymbolOrderBook.cs
index 886e39b..9cf4f2d 100644
--- a/CryptoExchange.Net/Interfaces/ISymbolOrderBook.cs
+++ b/CryptoExchange.Net/Interfaces/ISymbolOrderBook.cs
@@ -10,6 +10,11 @@ namespace CryptoExchange.Net.Interfaces
     /// </summary>
     public interface ISymbolOrderBook
     {
+        /// <summary>
+        /// Identifier
+        /// </summary>
+        string Id { get; }
+
         /// <summary>
         /// The status of the order book. Order book is up to date when the status is `Synced`
         /// </summary>