Valve recommends you sit down for this announcement, though you might also want to jump into the air and yell in excitement. If you really like playing Portal 2 co-op, that is (and who doesn't?). The ...

Valve has opened up Portal 2's Perpetual Testing Initiative - mod tools for user-created levels - to co-operative play. Previously, user-generated levels were restricted to single-player only, which ...

Since Valve introduced co-op play to Portal 2, it’s fair to say that the mind-bending physics puzzler’s brought people together. But Gary Hudston had something even more permanent in mind. As he tells ...

Portal 2's level creation DLC, the "Perpetual Testing Initiative", goes live today on Steam, and it's totally free. So would-be Aperture scientists can get cracking on designing new tests and sharing ...