How do I take a screen shot using Mac OS X?

Take screenshot of entire screen and save to desktop as PNG file.

Command-Shift-3    

  

Take a screenshot of part of the screen using crosshair selector and save to desktop as PNG file.

Command-Shift-4

Take a screenshot of a Window and save to desktop as PNG file.
Command-Shift-4, tap Spacebar, click inside a Window. 

To copy the image to the clipboard instead of saving it to a file, add a Shift key.

Command-Control-Shift-3

Command-Control-Shift-4

Command-Shift-4, tap Spacebar, click inside a Window.