This book challenges standard notions of expertise. In today's world, truly effective expertise is built on fluid collaboration between practitioners from multiple backgrounds. Such collaborative expertise must also be transformative, must be able to tackle emerging new problems and changes in its organizational framework. Engeström argues that the transition toward collaborative and transformative expertise is based on three pillars: expertise needs to be understood and cultivated as a collective activity; expertise needs to be built on flexible knot-working among diverse practitioners; and expertise needs to be fostered as the expansive learning of models and patterns of activity that are in progress. In this book, Engeström recasts expertise as fluid collaboration on complex tasks that requires envisioning the future and mastering change.