diff --git a/SeatsioDotNet.Test/ErrorHandlingTest.cs b/SeatsioDotNet.Test/ErrorHandlingTest.cs
index a4d931b..27ec8ce 100644
--- a/SeatsioDotNet.Test/ErrorHandlingTest.cs
+++ b/SeatsioDotNet.Test/ErrorHandlingTest.cs
@@ -19,7 +19,7 @@ public void Test4xx()
         public void WeirdError()
         {
             var e = Assert.Throws<SeatsioException>(() =>
-                new SeatsioClient("", "unknownProtocol://").Events.RetrieveObjectStatus("unexistingEvent", "unexistingObject"));
+                new SeatsioClient("", null, "unknownProtocol://").Events.RetrieveObjectStatus("unexistingEvent", "unexistingObject"));
 
             Assert.Equal("GET  resulted in a 0  response.", e.Message);
             Assert.Null(e.Errors);
diff --git a/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs b/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs
index 352d7f3..81a6095 100644
--- a/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs
+++ b/SeatsioDotNet.Test/HoldTokens/RetrieveHoldTokenTest.cs
@@ -14,6 +14,7 @@ public void Test()
             Assert.Equal(holdToken.Token, retrievedHoldToken.Token);
             Assert.Equal(holdToken.ExpiresAt, retrievedHoldToken.ExpiresAt);
             Assert.InRange(holdToken.ExpiresInSeconds, 14 * 60, 15 * 60);
+            Assert.NotNull(holdToken.workspaceKey);
         }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet.Test/SeatsioClientTest.cs b/SeatsioDotNet.Test/SeatsioClientTest.cs
index b6efa89..c2bd2da 100644
--- a/SeatsioDotNet.Test/SeatsioClientTest.cs
+++ b/SeatsioDotNet.Test/SeatsioClientTest.cs
@@ -64,7 +64,12 @@ protected string CreateTestChartFromJson(String json)
 
         protected SeatsioClient CreateSeatsioClient(string secretKey)
         {
-            return new SeatsioClient(secretKey, BaseUrl);
+            return new SeatsioClient(secretKey, null, BaseUrl);
+        }
+
+        protected SeatsioClient CreateSeatsioClient(string secretKey, string workspaceKey)
+        {
+            return new SeatsioClient(secretKey, workspaceKey, BaseUrl);
         }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs b/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs
index d96197b..96b6c52 100644
--- a/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs
+++ b/SeatsioDotNet.Test/Subaccounts/RetrieveSubaccountTest.cs
@@ -17,6 +17,7 @@ public void Test()
             Assert.Equal(subaccount.PublicKey, retrievedSubaccount.PublicKey);
             Assert.Equal("joske", retrievedSubaccount.Name);
             Assert.True(retrievedSubaccount.Active);
+            Assert.NotNull(retrievedSubaccount.workspaceKey);
         }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet.Test/WorkspaceKeyAuthenticationTest.cs b/SeatsioDotNet.Test/WorkspaceKeyAuthenticationTest.cs
new file mode 100644
index 0000000..02cb08e
--- /dev/null
+++ b/SeatsioDotNet.Test/WorkspaceKeyAuthenticationTest.cs
@@ -0,0 +1,18 @@
+using Xunit;
+
+namespace SeatsioDotNet.Test
+{
+    public class WorkspaceKeyAuthenticationTest : SeatsioClientTest
+    {
+        [Fact]
+        public void Test()
+        {
+            var subaccount = Client.Subaccounts.Create();
+
+            var subaccountClient = CreateSeatsioClient(User.SecretKey, subaccount.workspaceKey);
+            var holdToken = subaccountClient.HoldTokens.Create();
+
+            Assert.Equal(subaccount.workspaceKey, holdToken.workspaceKey);
+        }
+    }
+}
\ No newline at end of file
diff --git a/SeatsioDotNet/HoldTokens/HoldToken.cs b/SeatsioDotNet/HoldTokens/HoldToken.cs
index 3c27fbf..dc7e713 100644
--- a/SeatsioDotNet/HoldTokens/HoldToken.cs
+++ b/SeatsioDotNet/HoldTokens/HoldToken.cs
@@ -9,5 +9,6 @@ public class HoldToken
         public string Token { get; set; }
         public DateTimeOffset ExpiresAt { get; set; }
         public int ExpiresInSeconds { get; set; }
+        public string workspaceKey { get; set; }
     }
 }
\ No newline at end of file
diff --git a/SeatsioDotNet/SeatsioClient.cs b/SeatsioDotNet/SeatsioClient.cs
index a624a90..7761c83 100644
--- a/SeatsioDotNet/SeatsioClient.cs
+++ b/SeatsioDotNet/SeatsioClient.cs
@@ -14,9 +14,9 @@ public class SeatsioClient
         public ChartReports.ChartReports ChartReports { get; }
         public UsageReports.UsageReports UsageReports { get; }
 
-        public SeatsioClient(string secretKey, string baseUrl)
+        public SeatsioClient(string secretKey, string workspaceKey, string baseUrl)
         {
-            var restClient = CreateRestClient(secretKey, baseUrl);
+            var restClient = CreateRestClient(secretKey, workspaceKey, baseUrl);
             Charts = new Charts.Charts(restClient);
             Events = new Events.Events(restClient);
             Accounts = new Accounts.Accounts(restClient);
@@ -27,14 +27,23 @@ public SeatsioClient(string secretKey, string baseUrl)
             UsageReports = new UsageReports.UsageReports(restClient);
         }
 
-        public SeatsioClient(string secretKey): this(secretKey, "https://api.seatsio.net")
+        public SeatsioClient(string secretKey, string workspaceKey) : this(secretKey, workspaceKey, "https://api.seatsio.net")
         {
         }
 
-        private static RestClient CreateRestClient(string secretKey, string baseUrl)
+        public SeatsioClient(string secretKey) : this(secretKey, null)
+        {
+        }
+
+        private static RestClient CreateRestClient(string secretKey, string workspaceKey, string baseUrl)
         {
             var client = new RestClient(baseUrl);
             client.Authenticator = new HttpBasicAuthenticator(secretKey, null);
+            if (workspaceKey != null)
+            {
+                client.AddDefaultHeader("X-Workspace-Key", workspaceKey.ToString());
+            }
+
             return client;
         }
     }
diff --git a/SeatsioDotNet/Subaccounts/Subaccount.cs b/SeatsioDotNet/Subaccounts/Subaccount.cs
index bf772f7..5173acb 100644
--- a/SeatsioDotNet/Subaccounts/Subaccount.cs
+++ b/SeatsioDotNet/Subaccounts/Subaccount.cs
@@ -3,6 +3,7 @@
     public class Subaccount
     {
         public long Id { get; set; }
+        public string workspaceKey { get; set; }
         public string SecretKey { get; set; }
         public string DesignerKey { get; set; }
         public string PublicKey { get; set; }