diff --git a/library/src/main/java/io/constructor/core/Constants.kt b/library/src/main/java/io/constructor/core/Constants.kt
index 714ee902..6b5d0949 100755
--- a/library/src/main/java/io/constructor/core/Constants.kt
+++ b/library/src/main/java/io/constructor/core/Constants.kt
@@ -24,6 +24,7 @@ class Constants {
         const val NUM_RESULTS = "num_results_"
         const val GROUP_ID = "group[group_id]"
         const val GROUP_DISPLAY_NAME = "group[display_name]"
+        const val USER_ID = "ui"
     }
 
     object QueryValues {
diff --git a/library/src/main/java/io/constructor/core/ConstructorIo.kt b/library/src/main/java/io/constructor/core/ConstructorIo.kt
index 44e98f21..99ee9117 100755
--- a/library/src/main/java/io/constructor/core/ConstructorIo.kt
+++ b/library/src/main/java/io/constructor/core/ConstructorIo.kt
@@ -32,6 +32,12 @@ object ConstructorIo {
     private lateinit var context: Context
     private var disposable = CompositeDisposable()
 
+    var userId: String?
+        get() = configMemoryHolder.userId
+        set(value) {
+            configMemoryHolder.userId = value
+        }
+
     internal val component: AppComponent by lazy {
         DaggerAppComponent.builder()
                 .appModule(AppModule(context))
diff --git a/library/src/main/java/io/constructor/data/interceptor/TokenInterceptor.kt b/library/src/main/java/io/constructor/data/interceptor/TokenInterceptor.kt
index fe2151f0..98e5cc09 100755
--- a/library/src/main/java/io/constructor/data/interceptor/TokenInterceptor.kt
+++ b/library/src/main/java/io/constructor/data/interceptor/TokenInterceptor.kt
@@ -23,6 +23,9 @@ class TokenInterceptor(val context: Context, private val preferencesHelper: Pref
                 builder.addQueryParameter(it.first, it.second)
             }
         }
+        configMemoryHolder.userId?.let {
+            builder.addQueryParameter(Constants.QueryConstants.USER_ID, it)
+        }
         val url = builder.build()
         request = request.newBuilder().url(url).build()
         return chain.proceed(request)
diff --git a/library/src/main/java/io/constructor/data/memory/ConfigMemoryHolder.kt b/library/src/main/java/io/constructor/data/memory/ConfigMemoryHolder.kt
index 71f516d1..67b89d86 100644
--- a/library/src/main/java/io/constructor/data/memory/ConfigMemoryHolder.kt
+++ b/library/src/main/java/io/constructor/data/memory/ConfigMemoryHolder.kt
@@ -33,4 +33,6 @@ class ConfigMemoryHolder @Inject constructor() {
         }
 
     var autocompleteResultCount: Map<String, Int>? = null
+
+    var userId: String? = null
 }
\ No newline at end of file
diff --git a/library/src/test/java/io/constructor/core/ConstructorIoTest.kt b/library/src/test/java/io/constructor/core/ConstructorIoTest.kt
index 949d884c..b7656db5 100755
--- a/library/src/test/java/io/constructor/core/ConstructorIoTest.kt
+++ b/library/src/test/java/io/constructor/core/ConstructorIoTest.kt
@@ -212,6 +212,7 @@ class ConstructorIoTest {
         every { pref.token } returns "123"
         every { pref.id } returns "1"
         every { configMemoryHolder.testCellParams = any() } just Runs
+        every { configMemoryHolder.userId } returns "uid"
         every { configMemoryHolder.autocompleteResultCount } returns mapOf(Constants.QueryValues.SEARCH_SUGGESTIONS to 10, Constants.QueryValues.PRODUCTS to 0)
         every { configMemoryHolder.testCellParams } returns listOf("ef-1" to "2", "ef-3" to "4")
         mockServer.start()
@@ -220,6 +221,7 @@ class ConstructorIoTest {
         client.newCall(Request.Builder().url(mockServer.url("/")).build()).execute()
         var recordedRequest = mockServer.takeRequest()
         assert(recordedRequest.path.contains("ef-1=2"))
+        assert(recordedRequest.path.contains("ui=uid"))
     }
 
     @Test
diff --git a/sample/src/main/java/io/constructor/sample/SampleApp.kt b/sample/src/main/java/io/constructor/sample/SampleApp.kt
index 5bfacc5c..03a9ff29 100755
--- a/sample/src/main/java/io/constructor/sample/SampleApp.kt
+++ b/sample/src/main/java/io/constructor/sample/SampleApp.kt
@@ -10,5 +10,6 @@ class SampleApp : Application() {
         super.onCreate()
         ConstructorIo.init(this, ConstructorIoConfig("key_OucJxxrfiTVUQx0C",
                 testCells = listOf("ab" to "cd", "11" to "22")))
+        ConstructorIo.userId = "uid"
     }
 }
\ No newline at end of file