Mountain Lion’s AirPlay Mirroring feature lets you wirelessly share your entire Mac’s desktop on an HDTV, using an Apple TV (second generation or later). Just as with iOS devices, you can use AirPlay to share photos and videos, or even stream games to your TV. AirPlay can also come in handy for giving presentations in a classroom or conference room.
AirPlay Mirroring is designed to work on the following Macs: iMac (Mid 2011 or newer), Mac mini (Mid 2011 or newer), MacBook Air (Mid 2011 or newer), and the MacBook Pro (Early 2011 or newer). Here’s how to get started.
Bonus Tip: To use AirPlay Mirroring on older Macs, take a look at a $9.99 app, AirParrot, which adds similar functionality for both Macs and PCs.