Organizing services in an integrated network as a model for transforming healthcare systems is often presented as a potential remedy for service fragmentation that should enhance system efficiency. In the mental health sector, integration is also part of a diversified response to the multiple needs of the clients, particularly people with serious mental health disorders. The authors describe how the notion of integrated service networks came to serve as a model for transforming the mental health system in Quebec, and they propose a frame of reference for this notion. They also address the challenges and issues raised by this mode of service organization in the mental health sector and more generally in a context of transforming healthcare systems.