Keyboard shortcut of MAC OS

To use a keyboard shortcut, or key combination, you press a modifier key with a character key. For example, pressing the Command key (the key with a symbol) and the "c" key at the same time copies whatever is currently selected (text, graphics, and so forth) into the Clipboard. This is also known as the Command-C key combination (or keyboard shortcut).
A modifier key is a part of many key combinations. A modifier key alters the way other keystrokes or mouse clicks are interpreted by Mac OS X. Modifier keys include: Command, Control, Option, Shift, Caps Lock, and the fn key (if your keyboard has a fn key).

Here are the modifier key symbols you can see in Mac OS X menus:
(Command key) - On some Apple keyboards, this key also has an Apple logo ()
 (Control key)
 (Option key) - "Alt" may also appear on this key
 (Shift key)
(Caps Lock) - Toggles Caps Lock on or off
fn (Function key)
Startup keyboard shortcuts
Press the key or key combination until the expected function occurs/appears (for example, hold Option during startup until Startup Manager appears, or Shift until "Safe Boot" appears). Tip: If a startup function doesn't work and you use a third-party keyboard, connect an Apple keyboard and try again.

Key or key combination	What it does
Option	Display all bootable volumes (Startup Manager)
Shift	Perform Safe Boot (start up in Safe Mode)
C	Start from a bootable disc (DVD, CD)
T	Start in FireWire target disk mode
N	Start from NetBoot server
X	Force Mac OS X startup (if non-Mac OS X startup volumes are present)
Command-V	Start in Verbose Mode
Command-S	Start in Single User Mode

Finder keyboard shortcuts

Key combination	What it does
Command-A	Select all items in the front Finder window (or desktop if no window is open)
Option-Command-A	Deselect all items
Shift-Command-A	Open the Applications folder
Command-C	Copy selected item/text to the Clipboard
Shift-Command-C	Open the Computer window
Command-D	Duplicate selected item
Shift-Command-D	Open desktop folder
Command-E	Eject
Command-F	Find any matching Spotlight attribute
Shift-Command-F	Find Spotlight file name matches
Option-Command-F	Navigate to the search field in an already-open Spotlight window
Shift-Command-G	Go to Folder
Shift-Command-H	Open the Home folder of the currently logged-in user account
Command-I	Get Info
Option-Command-I	Show Inspector
Control-Command-I	Get Summary Info
Shift-Command-I	Open iDisk
Command-J	Show View Options
Command-K	Connect to Server
Shift-Command-K	Open Network window
Command-L	Make alias of the selected item
Command-M	Minimize window
Option-Command-M	Minimize all windows
Command-N	New Finder window
Shift-Command-N	New folder
Option-Command-N	New Smart Folder
Command-O	Open selected item
Shift-Command-Q	Log Out
Option-Shift-Command-Q	Log Out immediately
Command-R	Show original (of alias)
Command-T	Add to Sidebar
Shift-Command-T	Add to Favorites
Option-Command-T	Hide Toolbar / Show Toolbar in Finder windows
Shift-Command-U	Open Utilities folder
Command-V	Paste
Command-W	Close window
Option-Command-W	Close all windows
Command-X	Cut
Option-Command-Y	Slideshow (Mac OS X 10.5 or later)
Command-Z	Undo / Redo
Command-1	View as Icon
Command-2	View as List
Command-3	View as Columns
Command-4	View as Cover Flow (Mac OS X 10.5 or later)
Command-, (Command and the comma key)	Open Finder preferences
Command-` (the Grave accent key--above Tab key on a US English keyboard layout)	Cycle through open Finder windows
Command-Shift-?	Open Mac Help
Option-Shift-Command-Esc (hold for three seconds) - Mac OS X v10.5, v10.6 or later only	Force Quit front-most application
Command-[	Back
Command-]	Forward
Command-Up Arrow	Open enclosed folder
Control-Command-Up Arrow	Open enclosed folder in a new window
Command-Down Arrow	Open highlighted item
Command-Tab	Switch application--cycle forward
Shift-Command-Tab	Switch application--cycle backward
Command-Delete	Move to Trash
Shift-Command-Delete	Empty Trash
Option-Shift-Command-Delete	Empty Trash without confirmation dialog
Spacebar (or Command-Y)	Quick Look (Mac OS X 10.5 or later)
Command key while dragging	Move dragged item to other volume/location (pointer icon changes while key is held--see this article)
Option key while dragging	Copy dragged item (pointer icon changes while key is held--see this article)
Option-Command key combination while dragging	Make alias of dragged item (pointer icon changes while key is held--see this article)

Application and other Mac OS X keyboard commands
Note: Some applications may not support all of the below application key combinations.

Key combination	What it does
Command-Space	Show or hide the Spotlight search field (if multiple languages are installed, may rotate through enabled script systems)
Control-A	Move to beginning of line/paragraph
Control-B	Move one character backward
Control-D	Delete the character in front of the cursor
Control-E	Move to end of line/paragraph
Control-F	Move one character forward
Control-H	Delete the character behind the cursor
Control-K	Delete from the character in front of the cursor to the end of the line/paragraph
Control-L	Center the cursor/selection in the visible area
Control-N	Move down one line
Control-O	Insert a new line after the cursor
Control-P	Move up one line
Control-T	Transpose the character behind the cursor and the character in front of the cursor
Control-V	Move down one page
Option-Command-Space	Show the Spotlight search results window (if multiple languages are installed, may rotate through keyboard layouts and input methods within a script)
Command-Tab	Move forward to the next most recently used application in a list of open applications
Shift-Command-Tab	Move backward through a list of open applications (sorted by recent use)
Shift-Tab	Navigate through controls in a reverse direction
Control-Tab	Move focus to the next grouping of controls in a dialog or the next table (when Tab moves to the next cell)
Shift-Control-Tab	Move focus to the previous grouping of controls
Command-esc	Open Front Row (if installed)
Option-Eject	Eject from secondary optical media drive (if one is installed)
Control-Eject	Show shutdown dialog
Option-Command-Eject	Put the computer to sleep
Control-Command-Eject	Quit all applications (after giving you a chance to save changes to open documents), then restart the computer
Control Option-Command-Eject	Quit all applications (after giving you a chance to save changes to open documents), then shut down the computer
fn-Delete	Forward Delete (on portable Macs' built-in keyboard)
Control-F1	Toggle full keyboard access on or off
Control-F2	Move focus to the menu bar
Control-F3	Move focus to the Dock
Control-F4	Move focus to the active (or next) window
Shift-Control-F4	Move focus to the previously active window
Control-F5	Move focus to the toolbar.
Control-F6	Move focus to the first (or next) panel
Shift-Control-F6	Move focus to the previous panel
Control-F7	Temporarily override the current keyboard access mode in windows and dialogs
F9	Tile or untile all open windows
F10	Tile or untile all open windows in the currently active application
F11	Hide or show all open windows
F12	Hide or display Dashboard
Command-`	Activate the next open window in the frontmost application
Shift-Command-`	Activate the previous open window in the frontmost application
Option-Command-`	Move focus to the window drawer
Command- - (minus)	Decrease the size of the selected item
Command-{	Left-align a selection
Command-}	Right-align a selection
Command-|	Center-align a selection
Command-:	Display the Spelling window
Command-;	Find misspelled words in the document
Command-,	Open the front application's preferences window (if it supports this keyboard shortcut)
Option-Control-Command-,	Decrease screen contrast
Option-Control-Command-.	Increase screen contrast
Command-?	Open the application's help in Help Viewer
Option-Command-/	Turn font smoothing on or off
Shift-Command-=	Increase the size of the selected item
Shift-Command-3	Capture the screen to a file
Shift-Control-Command-3	Capture the screen to the Clipboard
Shift-Command-4	Capture a selection to a file
Shift-Control-Command-4	Capture a selection to the Clipboard
Command-A	Highlight every item in a document or window, or all characters in a text field
Command-B	Boldface the selected text or toggle boldfaced text on and off
Command-C	Copy the selected data to the Clipboard
Shift-Command-C	Display the Colors window
Option-Command-C	Copy the style of the selected text
Control-Command-C	Copy the formatting settings of the selected item and store on the Clipboard
Option-Command-D	Show or hide the Dock
Command-Control D	Display the definition of the selected word in the Dictionary application
Command-E	Use the selection for a find
Command-F	Open a Find window
Option-Command-F	Move to the search field control
Command-G	Find the next occurrence of the selection
Shift-Command-G	Find the previous occurrence of the selection
Command-H	Hide the windows of the currently running application
Option-Command-H	Hide the windows of all other running applications
Command-I	Italicize the selected text or toggle italic text on or off
Option-Command-I	Display an inspector window
Command-J	Scroll to a selection
Command-M	Minimize the active window to the Dock
Option-Command-M	Minimize all windows of the active application to the Dock
Command-N	Create a new document in the frontmost application
Command-O	Display a dialog for choosing a document to open in the frontmost application
Command-P	Display the Print dialog
Shift-Command-P	Display a dialog for specifying printing parameters (Page Setup)
Command-Q	Quit the frontmost application
Command-S	Save the active document
Shift-Command-S	Display the Save As dialog
Command-T	Display the Fonts window
Option-Command-T	Show or hide a toolbar
Command-U	Underline the selected text or turn underlining on or off
Command-V	Paste the Clipboard contents at the insertion point
Option-Command-V	Apply the style of one object to the selected object (Paste Style)
Option-Shift-Command-V	Apply the style of the surrounding text to the inserted object (Paste and Match Style)
Control-Command-V	Apply formatting settings to the selected object (Paste Ruler Command)
Command-W	Close the frontmost window
Shift-Command-W	Close a file and its associated windows
Option-Command-W	Close all windows in the application without quitting it
Command-X	Remove the selection and store in the Clipboard
Command-Z	Undo previous command (some applications allow for multiple Undos)
Shift-Command-Z	Redo previous command (some applications allow for multiple Redos)
Control-Right Arrow	Move focus to another value or cell within a view, such as a table
Control-Left Arrow	Move focus to another value or cell within a view, such as a table
Control-Down Arrow	Move focus to another value or cell within a view, such as a table
Control-Up Arrow	Move focus to another value or cell within a view, such as a table
Command-Right Arrow	Move the text insertion point to the end of the current line
Command-Left Arrow	Move the text insertion point to the beginning of the current line
Command-Down Arrow	Move the text insertion point to the end of the document
Command-Up Arrow	Move the text insertion point to the beginning of the document
Shift-Command-Right Arrow	Select text between the insertion point and the end of the current line (*)
Shift-Command-Left Arrow	Select text between the insertion point and the beginning of the current line (*)
Shift-Right Arrow	Extend text selection one character to the right (*)
Shift-Left Arrow	Extend text selection one character to the left (*)
Shift-Command-Up Arrow	Select text between the insertion point and the beginning of the document (*)
Shift-Command-Down Arrow	Select text between the insertion point and the end of the document (*)
Shift-Up Arrow	Extend text selection to the line above, to the nearest character boundary at the same horizontal location (*)
Shift-Down Arrow	Extend text selection to the line below, to the nearest character boundary at the same horizontal location (*)
Shift-Option-Right Arrow	Extend text selection to the end of the current word, then to the end of the following word if pressed again (*)
Shift-Option-Left Arrow	Extend text selection to the beginning of the current word, then to the beginning of the following word if pressed again (*)
Shift-Option-Down Arrow	Extend text selection to the end of the current paragraph, then to the end of the following paragraph if pressed again (*)
Shift-Option-Up Arrow	Extend text selection to the beginning of the current paragraph, then to the beginning of the following paragraph if pressed again (*)
Control-Space	Toggle between the current and previous input sources
Option-Control-Space	Toggle through all enabled input sources
Option-Command-esc	Force Quit

(*) Note: If no text is selected, the extension begins at the insertion point. If text is selected by dragging, then the extension begins at the selection boundary. Reversing the direction of the selection deselects the appropriate unit.

Universal Access - VoiceOver keyboard commands
For information about VoiceOver key combination differences in Mac OS X v10.6, see this article.

Key combination	What it does
Command-F5 or fn Command-F5	Turn VoiceOver on or off
Control Option-F8 or fn Control Option-F8	Open VoiceOver Utility
Control Option-F7 or fn Control Option-F7	Display VoiceOver menu
Control Option-; or fn Control Option-;	Enable/disable VoiceOver Control Option-lock
Option-Command-8 or fn Command-F11	Turn on Zoom
Option-Command-+	Zoom In
Option-Command- - (minus)	Zoom Out
Option-Control-Command-8	Invert/revert the screen colors
Control Option-Command-,	Reduce contrast
Control Option-Command-.	Increase contrast

Note: You may need to enable "Use all F1, F2, etc. keys as standard keys" in Keyboard preferences for the VoiceOver menu and utility to work.

Universal Access - Mouse Keys
When Mouse Keys is turned on in Universal Access preferences, you can use the keyboard or numeric keypad keys to move the mouse pointer. If your computer doesn't have a numeric keypad, use the Fn (function) key.

Key combination	What it does
8	Move Up
2	Move Down
4	Move Left
6	Move Right
1	Move Diagonally Bottom Left
3	Move Diagonally Bottom Right
7	Move Diagonally Top Left
9	Move Diagonally Top Right
5	Press Mouse Button
0	Hold Mouse Button
. (period on number pad)	Release Hold Mouse Button