This book brings together contributions from researchers within various social science disciplines who seek to redefine the methods and topics that constitute the study of work. They investigate work activity in ways that do not reduce it to a 'psychology' of individual cognition nor to a 'sociology' of societal structures and communication. A key theme in the material is the relationship between theory and practice. This is not an abstract problem of interest merely to social scientists. Rather, it is discussed as an issue that working people address when they attempt to understand a task and communicate its demands. Mindful practices and communicative interaction are examined as situated issues at work in the reproduction of communities of practice in a variety of settings including: courts of law, computer software design, the piloting of airliners, the coordination of air traffic control, and traffic management in underground railway systems.