Yes, Portal 2 does indeed have a co-op mode which allows you to play with a friend either locally (split-screen) or online. Here's how you can access it: 1. ONLINE CO-OP: To play Portal 2 co-op mode online, you'll need to have a friend who also owns the game. This is because Portal 2 co-op is a separate mode with its own unique levels requiring two players, with each player controlling a separate robot character (either Atlas or P-body). Here's the steps to begin an online co-op match: a. Launch the game and select 'Play Cooperatively' from the main menu. b. It will bring you to another menu where you will choose between 'Standard Cooperative Testing Courses' and the 'Challenge mode'. Pick as per your preference. c. Now you can invite your friend to join in by selecting their name from your friend list on the platform you are using (Steam, PS3, etc). 2. LOCAL (SPLIT-SCREEN) CO-OP: Portal 2 also supports split-screen co-op if you want to play with someone in the same room. This is only on console versions or if you're using Big Picture mode on PC. Here are the steps: a. Launch the game and select 'Play Cooperatively' from the main menu. b. On the next menu, select 'Standard Cooperative Testing Courses' or 'Challenge mode' as per your choice. c. Now choose 'Split Screen'. Connect the second controller and press X (or the corresponding button depending on your platform) to join the game. As a friendly sidebar for those new to the co-op mode, it is designed to be a little more challenging than the single player campaign and requires good teamwork, due to the puzzles being designed to need two players to solve. Happy gaming!