Depending on your Pro Tools software you will have a number of options. If you want to use Pro Tools then you can use any interface that supports Core Audio on Mac and ASIO on Windows. If you want to use Pro Tools HD then you will need to use an interface that has a DigiLink connection on it to connect to the Pro Tools HD or HDX cards, or via the Pro Tools HD Thunderbolt box.
What Kind Of Audio Interface Do You Use For Pro Tools? is a poll we conducted of Pro Tools users. Check it out to see the results.