using System.Threading;

    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        { 
            bool createdNew = true;
            using (Mutex mutex = new Mutex(true, "SignleInstance", out createdNew))
            {
                if (createdNew)
                {
                    Application.EnableVisualStyles();
                    Application.SetCompatibleTextRenderingDefault(false);
                    Application.Run(new Form1());
                }
            }
        }
    }

Download Single Instance Application Source Code

I still don’t get why in Visual Studio in VB.NET one could click make single instance application, but that same feature doesn’t exist in C#? Don’t all .NET languages just get compiled to the CIL in the end?