<Application x:Class="SingleInstanceSample.App" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" StartupUri="Window1.xaml"> <Application.Resources> </Application.Resources> </Application> //File:Window.xaml.cs using System; using System.Windows; using System.Data; using System.Xml; using System.Configuration; using System.Threading; using System.Reflection; namespace SingleInstanceSample { public partial class App : System.Windows.Application { Mutex mutex; protected override void OnStartup(StartupEventArgs e) { base.OnStartup(e); string mutexName = "MyCompanyName.MyAppName"; bool createdNew; mutex = new Mutex(true, mutexName, out createdNew); if( !createdNew ) { Shutdown(); } } } }