In C#, Windows Form is a User Interface (UI) that picks up input from the application users. An application can show these forms as either Modal Dialog or Modeless Dialog. Note, a Form can call some other Form and it can go deep nesting. In case of a Modal C# Dialog, the caller gets blocked till the user closes the Modal Dialog. Conversely, the Modeless C# Dialog does not block the caller. We explore these with an example.