Screen Capture Shortcuts

• Command-Shift-3:  screen capture of your entire screen, save to your desktop
• Command-Shift-4:  crosshair cursor so you can choose which area of the screen you want to capture, save to your desktop
• Adding Control to either of these commands copies the capture into your Clipboard memory, so you can paste it where you want.

via Apple – Pro – Tips – The Secret Screen Capture Shortcut.