This ground-breaking book brings together cutting-edge researchers who study the transformation of practice through the enhancement and transformation of expertise. This is an important moment for such a contribution because expertise is in transition - moving toward collaboration in inter-organizational fields and continuous shaping of transformations. To understand and master this transition, powerful new conceptual tools are needed and are provided here. The theoretical framework which has shaped these studies is Cultural Historical Activity Theory (CHAT). CHAT analyses how people and organisations learn to do something new, and how both individuals and organisations change. The theoretical and methodological tools used have their origins in the work of Lev Vygotsky and A.N. Leont'ev. In recent years this body of work has aroused significant interest across the social sciences, management and communication studies. Working as part of an integrated international team, the authors identify specific findings which are of direct interest to the academic community, such as: the analysis of vertical learning between operational and strategic levels within complex organizations; the refinement of notions of identity and subject position within CHAT; the introduction of the concept of 'labour power' into CHAT; the development of a method of analysing discourse which theoretically coheres with CHAT and the design of projects. Activity Theory in Practice will be highly useful to practitioners, researchers, students and policy-makers who are interested in conceptual and empirical issues in all aspects of 'activity-based' research.