Watson is a computer system capable of answering rich natural language questions and estimating its confidence in those answers at a level rivaling the best humans at the task. On Feb 14-16, 2011, in an historic event, Watson triumphed over the best Jeopardy! players of all time. This success was important in numerous ways, one of which is as a prominent exemplar of a new generation of computing systems, that we now call Cognitive Computing Systems. Cognitive computing involves a new synthesis of classic AI problems such as language understanding, image and video processing, with big data, human computing, and massive processing. Social systems are an important driver of cognitive computing, as they provide data used by many systems (dbpedia, freebase, twitter) as well as numerous potential applications. In this talk I will discuss how Watson works, and cognitive computing with an eye towards social computing.