Product-Service System (PSS) innovations represent a promising approach to sustainability, but their implementation and diffusion is hindered by several cultural, corporate and regulative barriers. Hence, an important challenge is not only to conceive sustainable PSS concepts, but also to understand how to manage, support and orient the introduction and diffusion of these concepts. Building upon insights from transition studies (in particular the concepts of Strategic Niche Management and Transition Management), and through an action research project, the chapter investigates the role of design in introducing sustainable radical service innovations. A key role is given to the implementation of socio-technical experiments, partially protected spaces where innovations can be incubated and tested, become more mature, and potentially favor the implementation and scaling up process.