This book describes, for the first time in pedagogical form, an approach to computer-based work in complex sociotechnical systems developed over the last 30 years by Jens Rasmussen and his colleagues at Risø National Laboratory in Roskilde, Denmark. This approach is represented by a framework called cognitive work analysis. Its goal is to help designers of complex sociotechnical systems create computer-based information support that helps workers adapt to the unexpected and changing demands of their jobs. In short, cognitive work analysis is about designing for adaptation. The book is divided into four parts. Part I provides a motivation by introducing three themes that tie the book together--safety, productivity, and worker health. The ecological approach that serves as the conceptual basis behind the book is also described. In addition, a glossary of terms is provided. Part II situates the ideas in the book in a broader intellectual context by reviewing alternative approaches to work analysis. The limitations of normative and descriptive approaches are outlined, and the rationale behind the formative approach advocated in this book is explored. Part III describes the concepts that comprise the cognitive work analysis framework in detail. Each concept is illustrated by a case study, and the implications of the framework for design and research are illustrated by example. Part IV unifies the themes of safety, productivity, and health, and shows why the need for the concepts in this book will only increase in the future. In addition, a historical addendum briefly describes the origins of the ideas described in the book.