Steam Holiday Sale, day 9: Assassin's Creed, Prototype, Left 4 Dead franchises and moreBy J. Mallory, 12.28.2012
Valve says NVIDIA's the best, Steam and Left 4 Dead for Linux coming along nicelyBy T. O'Brien, 08.02.2012
Payday: The Heist - No Mercy sets the scene for Left 4 Dead [Update: It's 'not canon,' Valve clarifies]By J. Fletcher, 06.15.2012
Payday dev collaborating with Valve on Left 4 Dead 'co-operative initiative'By B. Gilbert, 05.21.2012