2K Games and Valve Software have announced an agreement that will bring Civilization IV, Civilization III, Shattered Union, and Sid Meier's Pirates! to Steam.

"With titles from legendary designer Sid Meier and 2K's world renowned developer, Firaxis Games, 2K is one of today's foremost publishers," said Gabe Newell, co-founder and president of Valve. "Through this initial agreement with 2K, Steam's game library expands to include four great strategy games. We look forward to delivering more from 2K in the future."

"We are excited to add Valve to our roster of partners in the digital distribution area," said Paul Crockett, Strategic Sales and Licensing, 2K. "Being included in their vast network will assist us in expanding the reach of our products to a much larger audience."

I'll add my own quote to this story: "Valve is becoming the iTunes of the gaming world." That should be pretty obvious to all steam users at this point.