MacOS – Is it possible to continue using an to external monitor when closing the lid on a Macbook Air

edit: See this as the behaviour has changed: Why won't closing the lid sleep my MacBook Pro with external monitor attached after upgrading to Lion?

There are two groups of people. Those who wish to have dual displays and have closing the lid go into sleep and people who wish to disable the monitor display, close the lid and use the external monitor as if you had 'docked' with it.

Previously, if you wished to switch from the macbook to an external monitor entirely then you had to perform the following to put the laptop into clamshell mode:

1. Make sure the computer is plugged in to an outlet using the AC power adapter.
2. Connect a USB keyboard and mouse to your computer.
3. With the computer turned on connect the Apple portable (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
4. Once your computer's Desktop appears on the external display, close the computer's lid.
5. Once the lid is closed, wake the computer up by either clicking your mouse button or by pressing a key on your external keyboard.

source: http://support.apple.com/kb/ht3131

So to put the machine in clamshell mode required you to put it to sleep and wake it back up again. As far as user experience goes, that is somewhat jarring.

As you have the other options to put the machine to sleep, it seems very likely that this change will remain.

Right now, there is no way to alter this behaviour.

According to Apple Support, the clamshell mode (lid closed) requires:

• Power adapter
• External keyboard, mouse, or trackpad
• External display

You meet all three criteria. The support article goes on to provide steps for both wired and bluetooth keyboard & mouse combos:

If you are using a wired keyboard and mouse:

1. Make sure the computer is plugged in to an outlet using the AC power adapter.
2. Connect a USB keyboard and mouse to your computer.
3. With the computer turned on connect the Apple portable (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
4. After your computer's Desktop appears on the external display, close the computer's lid.
5. When you close the lid:
   • In OS X Lion, the external display will change to a blue screen, then will show your desktop.
   • In Mac OS X v10.6.8 and earlier, wake the computer up by clicking the mouse button or by pressing a key on your external keyboard. You should now be able to use your Apple portable as you normally would, with a USB keyboard and mouse.

Perhaps you could try opening and closing the lid again.