Example of using a Mutex to determine if .NET application is already running

dotNetMutex.cs

bool mutexIsNew;
using (System.Threading.Mutex m =
  new System.Threading.Mutex(true, uniqueName, out mutexIsNew))
{
  if (mutexIsNew)
    // This is the first instance. Run the application.
  else
    // There is already an instance running. Exit!
}