diff --git a/src/src/AfasBase.cs b/src/src/AfasBase.cs
index 5d6382a..2f6895b 100644
--- a/src/src/AfasBase.cs
+++ b/src/src/AfasBase.cs
@@ -19,6 +19,8 @@ public class AfasBase : GeneralBase
 
         protected string Token64 { get; set; }
 
+        protected string IntegrationId { get; set; }
+
         protected override string GetBaseUrl
         {
             get
@@ -38,6 +40,7 @@ protected override async Task<HttpResponseMessage> GetAuthHttp(string urlPath)
                 }
             })
             {
+                AddIntegrationId(httpRequestMessage);
                 return await httpClient.SendAsync(httpRequestMessage);
             }
         }
@@ -55,6 +58,7 @@ protected override async Task<HttpResponseMessage> SendAuthHttp(string urlPath,
                 Content = new StringContent(content)                
             })
             {
+                AddIntegrationId(httpRequestMessage);
                 return await httpClient.SendAsync(httpRequestMessage);
             }
         }
@@ -72,6 +76,15 @@ protected override async Task<HttpResponseMessage> OtpPost(string urlPath, strin
             }
         }
 
+        private void AddIntegrationId(HttpRequestMessage httpRequestMessage)
+        {
+            if (httpClient.DefaultRequestHeaders.Contains("IntegrationId"))
+                httpClient.DefaultRequestHeaders.Remove("IntegrationId");
+            if (!string.IsNullOrWhiteSpace(this.IntegrationId))
+            {
+                httpRequestMessage.Headers.Add("IntegrationId", this.IntegrationId);
+            }
+        }
 
     }
 }
diff --git a/src/src/AfasClient.cs b/src/src/AfasClient.cs
index e44225a..47cbb20 100644
--- a/src/src/AfasClient.cs
+++ b/src/src/AfasClient.cs
@@ -10,14 +10,21 @@ namespace DutchGrit.Afas
 
     public class AfasClient : AfasBase, IAfasClient
     {
-
-        public AfasClient(int MemberNumber, string Token, Environments Env = Environments.Production, HttpClient customHttpClient=null)
+        /// <summary>
+        /// Constructor for the AfasClient
+        /// </summary>
+        /// <param name="integrationId">The integrationId to add as a request header. https://docs.afas.help/Profit/nl/IntegrationId</param>
+        /// <remarks>
+        /// Note: If a customHttpClient is provided, the integrationId header will be overwritten by the integrationId parameter.
+        /// </remarks>
+        public AfasClient(int MemberNumber, string Token, Environments Env = Environments.Production, HttpClient customHttpClient = null, string integrationId = null)
         {
             this.MemberNumber = MemberNumber;
             this.Environment = Env;
             //Convert the Token string into Base64.
             var authToken = Encoding.ASCII.GetBytes(Token);
             this.Token64 = "AfasToken " + Convert.ToBase64String(authToken);
+            this.IntegrationId = integrationId;
 
 
             if (customHttpClient != null)