Teams are commonly celebrated as efficient and humane ways of organizing work and learning. By means of a series of in-depth case studies of teams in the United States and Finland over a time span of more than ten years, this book shows that teams are not a universal and ahistorical form of collaboration. Teams are best understood in their specific activity contexts and embedded in historical development of work. The book develops a set of conceptual tools for analysis and design of transformations in collaborative work and learning.