This thesis aimed to explore the (cost-)effectiveness of preventive, integrated care for community-dwelling frail older people. The first part of this thesis focused on the effectiveness and cost-effectiveness of a specific preventive integrated care intervention, the Walcheren Integrated Care Model (WICM). The second part of this thesis critically reflected on the concepts and methodologies used to explore the (cost-)effectiveness of integrated care for frail older people. This second part included a systematic review and an exploration of the effectiveness of integrated care for six profiles of frail older people.