Here’s a basic MVVM compliant way of getting the behaviour you want: MainWindow.xaml <Window x:Class=”WpfApplication1.MainWindow” xmlns=”http://schemas.microsoft.com/winfx/2006/xaml/presentation” xmlns:x=”http://schemas.microsoft.com/winfx/2006/xaml” Title=”MainWindow” Height=”350″ Width=”525″> <StackPanel> <ComboBox Margin=”30,5,30,5″ IsEditable=”True” ItemsSource=”{Binding Items}” SelectedItem=”{Binding SelectedItem}” Text=”{Binding NewItem, UpdateSourceTrigger=LostFocus}”/> <TextBox Margin=”30,5,30,5″ /> </StackPanel> </Window> MainWindow.cs public partial class MainWindow : Window, INotifyPropertyChanged { private string _selectedItem; private ObservableCollection<string> _items = new ObservableCollection<string>() { … Read more