A modifier key modifies the action of another key when the keys are pressed at the same time. Common modifier keys include Shift, Function, Control, Alt, Command, and Option. The Shift key is found on all keyboards, while the other keys may be exclusive to laptops or Windows or Macintosh computers. Below is a list of the common modifier keys and their primary uses.

• Shift - used for capitalizing letters and entering different types of symbols.


• Function (Fn) - commonly found on laptop computers and used to enter the F1 - F15 commands if the function keys also have other functions (such as brightness and volume controls).


• Control (Ctrl) - a Windows key used for entering keyboard shortcuts, such as Ctrl+S for saving a file or Ctrl+P for printing a document.


• Alt - a Windows key that is also called the Alternate or Alternative key; used in combination with the numeric keypad for entering "Alt codes," which output special characters; may also be used in combination with the Control key for entering keyboard shortcuts.


• Command (Cmd) - a Macintosh key (similar to the Windows Control key) used for entering keyboard shortcuts; may have a four leaf clover or Apple icon printed on the key.


• Option - A Macintosh key (similar to the Windows Alt key) used for entering special characters; may also be used in combination with the Command key for entering keyboard shortcuts.

To enter a key combination that requires a modifier key, first press the modifier key, then the other key in the combination. For example, to save a document using the common "Ctrl+S" shortcut, first press and hold the Control key. Then press and release the "S" key to perform the command. Finally, release the Ctrl key. While most key combinations require only one modifier key, some require multiple modifier keys. For example, in Mac OS X, Cmd+Shift+3 takes a screenshot of the screen. In this case, either modifier key can be pressed first, as long as both keys are held when the "3" key is pressed.