diff --git a/MainWindow.axaml b/MainWindow.axaml
index a38647d..53ed631 100644
--- a/MainWindow.axaml
+++ b/MainWindow.axaml
@@ -154,6 +154,7 @@
                                         Margin="5,0,0,0">
                                 <Button HorizontalAlignment="Stretch" MinWidth="240"
                                         HorizontalContentAlignment="Center" x:Name="BtnCombineUnion"
+                                        Click="BtnCombineUnion_OnClick"
                                         Margin="0,0,0,10">
                                     <StackPanel Orientation="Horizontal">
                                         <LucideIcon Kind="SquaresUnite" Width="36" Height="36" />
diff --git a/MainWindow.axaml.cs b/MainWindow.axaml.cs
index 981dc46..777f0e8 100644
--- a/MainWindow.axaml.cs
+++ b/MainWindow.axaml.cs
@@ -240,14 +240,14 @@ public partial class MainWindow : Window
         }
     }
 
-    private async void StartDifference(List<KasAddressList> address_lists, int owner_id)
+    private async void StartCombine(List<KasAddressList> address_lists, int owner_id, string type)
     {
         var progressWindow = new ProgressWindow();
 
         progressWindow.Show(_instance);
 
         var processor = new CombineAddresses(progressWindow);
-        var result = await processor.Perform(address_lists, "difference");
+        var result = await processor.Perform(address_lists, type);
 
         result.owner_id = owner_id;
         Settings._instance.addressSets.addresses.Add(result);
@@ -258,6 +258,7 @@ public partial class MainWindow : Window
         //new ResultWindow(result, addresSetID).Show();
     }
 
+
     private void BtnSettingsAddCustomer_OnClick(object? sender, RoutedEventArgs e)
     {
         Settings._instance.customers.customers.Add(new Customer());
@@ -499,6 +500,16 @@ public partial class MainWindow : Window
             list.Add(Settings._instance.addressSets.GetAddressSetByID(
                 Convert.ToInt32(item.ToString().Split(" - ")[0])));
 
-        StartDifference(list, Convert.ToInt32(LstCustomers.SelectedItem.ToString().Split(" - ")[0]));
+        StartCombine(list, Convert.ToInt32(LstCustomers.SelectedItem.ToString().Split(" - ")[0]), "difference");
+    }
+
+    private void BtnCombineUnion_OnClick(object? sender, RoutedEventArgs e)
+    {
+        var list = new List<KasAddressList>();
+        foreach (var item in LstCustomerAdressSets.SelectedItems)
+            list.Add(Settings._instance.addressSets.GetAddressSetByID(
+                Convert.ToInt32(item.ToString().Split(" - ")[0])));
+
+        StartCombine(list, Convert.ToInt32(LstCustomers.SelectedItem.ToString().Split(" - ")[0]), "union");
     }
 }
\ No newline at end of file
diff --git a/Tasks/CombineAddresses.cs b/Tasks/CombineAddresses.cs
index d9fc293..aaaf76d 100644
--- a/Tasks/CombineAddresses.cs
+++ b/Tasks/CombineAddresses.cs
@@ -21,6 +21,7 @@ public class CombineAddresses
         var res = await Task.Run(async () =>
         {
             if (type == "difference") return Difference(address_lists);
+            if (type == "union") return Union(address_lists);
 
             return null;
         });
@@ -89,12 +90,12 @@ public class CombineAddresses
     }
 
     public async Task<KasAddressList> Difference(List<KasAddressList> address_lists,
-        DifferenceProgress? progress = null)
+        Progress? progress = null)
     {
         if (address_lists == null || address_lists.Count == 0)
             return new KasAddressList("difference");
 
-        progress ??= new DifferenceProgress
+        progress ??= new Progress
         {
             TotalPersons = address_lists.Sum(l => l.KasPersons.Count),
             ComparedPersons = 0
@@ -126,11 +127,41 @@ public class CombineAddresses
     }
 
 
-    public async Task<KasAddressList> Union()
+    public async Task<KasAddressList> Union(List<KasAddressList> address_lists, Progress progress = null)
     {
-        return null;
+        var result = new KasAddressList("union");
+
+        if (address_lists == null || address_lists.Count == 0)
+            return result;
+
+        var total = address_lists.Sum(l => l.KasPersons.Count);
+        var processed = 0;
+
+        foreach (var list in address_lists)
+        foreach (var person in list.KasPersons)
+        {
+            if (!result.KasPersons.Any(existing => CompareAddresses(existing, person)))
+                result.KasPersons.Add(person);
+
+            processed++;
+            var percent = processed / (double)total * 100;
+            var logMessage =
+                $"{percent:F1}%: Person mit {person.refsid} hinzugefügt (aktuell {result.KasPersons.Count} Einträge)";
+
+            // Sicher, nicht blockierend:
+            if (progress != null)
+            {
+                if (Dispatcher.UIThread.CheckAccess())
+                    progress.LogAction?.Invoke(logMessage);
+                else
+                    Dispatcher.UIThread.Post(() => progress.LogAction?.Invoke(logMessage));
+            }
+        }
+
+        return result;
     }
 
+
     public async Task<KasAddressList> MoveDuplicatesToNew()
     {
         return null;
@@ -207,7 +238,7 @@ public class CombineAddresses
     // }
 }
 
-public class DifferenceProgress
+public class Progress
 {
     public int TotalPersons { get; set; } // Gesamtzahl der zu prüfenden Personen
     public int ComparedPersons { get; set; } // Schon verglichene Personen