This is an old tip that many people don’t know, but is very useful.

  • If you want to take a screen shot of the entire screen, press Command(⌘)-Shift(⇧)-3.
  • If you want to take a screen shot of an area within the screen, press Command(⌘)-Shift(⇧)-4. The mouse will change into crosshairs. Drag a square around the area you want to capture in your image.
  • If you want to take a screen shot of a single window, press Command(⌘)-Shift(⇧)-4, then press the spacebar. The mouse will change into a camera, and clicking on a window will take a picture of the window.
There are a few additional behaviors when performing a Command(⌘)-Shift(⇧)-4 style area selection. All of these assume that you have clicked on a start point, and are dragging a box around the area you want selected, and must be held down to work.
  • The spacebar will allow you to reposition the rectangle.
  • Shift will allow you adjust either the width or the height of the rectangle without affecting the other dimension.
  • Option will allow you to adjust the size of the rectangle around its center point.
Finally, if you want to place the picture into the clipboard for pasting, rather than the default behavior of saving a file to the desktop, hold down the Control (⌃) key at the same time as the command(⌘)-shift(⇧)
combinations above.
Many people wonder why these command are mapped that way. In Mac OS Classic, Apple had the ability to assign actions to function keys. However, many Mac keyboards of the era did not have physical keys representing the function keys. Instead, Apple automatically mapped Command-Shift-number to act as Function key, and perform whatever task was assigned to it. These commands then were engrained into the muscle memories of Mac users, and the rest is history.
Oh, and lest I forget: To take a picture of the screen on an iOS device, press both the home key and the lock key at the same time.