

The host can make adjustments as to how the game will function for all players. The host can 'Eject' any player he doesn't want in the game by clicking the 'X' button next to the player's name they wish to eject. Once you are ready, you must select the ‘Ready’ button and then wait for the host to launch the game. If you have any further questions, please let us know - we will be happy to assist you.On this screen when playing as the host, you can select the map and game settings you wish to play with. Note: These methods are not supported, as split-screen is not an intended feature of the PC/Mac version of Portal 2. However, split-screen options may be available using the methods found here: Split-screen mode is available in the Xbox 360 and Playstation 3 versions of this game only. Steam Support indicates it's not supported, but also openly admits it's an option that currently exists. Valve has neither stated that this method is supported or banned.

It required modifying configuration files and a workaround to force the game to move a controller to the second player slot. It has been noted in the other answers that the act of single-system split-screen is possible. The game is still owned by only a single Steam account-another copy will be required to play online co-op with a friend. When you purchase a new copy of Portal 2 for PlayStation®3, you will receive an in-box code which provides your linked Steam account with access to your copy of Portal 2 on your computer. Only PlayStation®3 split-screen co-op can be played using a single copy of the game. The only way in which you can play co-op Portal 2 with a single Portal 2 purchase in a way that is obviously supported by the game manufacturer is by purchasing the PS3 copy:

Split-screen PC/Mac play is not supported by Valve via obvious in-game menus.
