How can I assign the 'Close on Escape-key press' behavior to all WPF windows within a project?

All I can suggest to improve on that is to remove the need for an event handler by binding to a static command instance.

Note: this will only work in .NET 4 onwards as it requires the ability to bind to the KeyBinding properties.

First, create a command that takes a Window as a parameter and calls Close within the Execute method:

public class CloseThisWindowCommand : ICommand{    #region ICommand Members    public bool CanExecute(object parameter)    {        //we can only close Windows        return (parameter is Window);    }    public event EventHandler CanExecuteChanged;    public void Execute(object parameter)    {        if (this.CanExecute(parameter))        {            ((Window)parameter).Close();        }    }    #endregion    private CloseThisWindowCommand()    {    }    public static readonly ICommand Instance = new CloseThisWindowCommand();}

Then you can bind your KeyBinding to the static Instance property:

<Window.InputBindings>    <KeyBinding Key="Escape" Command="{x:Static local:CloseThisWindowCommand.Instance}" CommandParameter="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=Window}}" /></Window.InputBindings>

I don't know that this is necessarily better than your approach, but it does mean marginally less boilerplate at the top of every Window and that you don't need to include an event handler in each

Or you could just add a button with Cancel as text and set IsCancel = True. Then Escape will work as default command to close.

create RoutedUICommand like below

 private static RoutedUICommand EscUICommand = new RoutedUICommand("EscBtnCommand"       , "EscBtnCommand"       , typeof(WindowName)       , new InputGestureCollection(new InputGesture[]            { new KeyGesture(Key.Escape, ModifierKeys.None, "Close") }));

and add it command binding in constructor

CommandBindings.Add(new CommandBinding(EscUICommand, (sender, e) => { this.Hide(); }));