Windows (PC)

Print Screen

Captures the entire screen to the clipboard.

Alt-Print Screen

Captures the active window to the clipboard.

Macintosh

Cmd-Shift-3

Takes a snapshot of the entire screen, (with camera sound effect!) and saves it automatically to the Hard Disk as Picture 1:

Subsequent screen shots will be stored as Picture 2, Picture 3, etc. (Double-clicking these files will open them in SimpleText format).

Cmd-Shift-4

Converts your cursor to a "cross-hair", allowing you to define a specific rectangular area of the screen to capture. This includes drop down menus, after you release the mouse button.

Cntrl-Cmd-Shift-4

Same as above, except the captured image is pasted to the Clipboard (rather than being stored as "Picture 1"). The image can then be pasted directly into a document.

Cmd-Shift-4-Caps Lock

Converts your cursor to a "target", allowing you to capture the active window. The image is stored as "Picture 1" etc on the HD.

Cntrl-Cmd-Shift-4-Caps Lock

As above, but capturing the active window to the clipboard. This image can then be pasted directly into a document.