This chapter is about group performance on problem-solving tasks, which is to say, cognitive endeavors that have as their goal the production of an objectively correct solution. These are also sometimes called intellective tasks, a term that refers broadly to their location on Laughlin’s IntellectiveJudgmental Task Continuum. As will be recalled from Chapter 2, Laughlin (1980, 1999; Laughlin & Ellis, 1986) suggested that cooperatively performed cognitive tasks can be meaningfully arrayed on a continuum anchored at one end by those that are purely intellective, and at the other by those that are purely judgmental. A purely intellective task is one where it is possible for group members to demonstrate to one another the correctness of a proposed solution (e.g., a simple arithmetic problem). A purely judgmental task, on the other hand, has no objectively correct solution (e.g., deciding whether Bach or Mozart was the greater composer). As such, on purely judgmental tasks it is impossible to conclusively demonstrate that one response is in fact better than another. The present chapter is concerned with group performance on tasks that are at or near the left-hand (intellective) end of this continuum.