From Wikipedia
Guerrilla Games is a first party video game developer and wholly owned subsidiary of Sony Computer Entertainment. The company is based out of Amsterdam in the Netherlands, currently employs approximately 140 individuals, and is headed by Managing Director Hermen Hulst and Development Director Arjan Brussee.
The developer is best known for its Killzone series; exclusive to Playstation. The most recent, Killzone 2, was released in February 2009 for the PlayStation 3. Guerrilla have confirmed that they are working on a third game in the series.