The implementation of innovative sustainability technologies often requires far-reaching changes of the macro environment in which the innovating firms operate. The chances of a successful diffusion and adoption of an innovative technology in society are increased if the firms wanting to commercialize this technology collaborate in networks or industry clusters to build a favorable environment for their technology. Entrepreneurs can strategically collaborate in networks of other technology producers, complimentary businesses, customers and government actors. By bundling their forces, they can accelerate the building up of a supportive innovation ecosystem or business ecosystem, in which their innovation can flourish. Combining the transition literature with insights from the strategic management literature, the concept of strategic collective system building has been formed. To underpin the theoretical analysis empirically, a case study in the Dutch smart grid field has been conducted. Based on this, a set of systemic strategy frameworks for system-building entrepreneurship have been developed. This is not only useful for a better theoretical understanding of collective action in emerging innovation ecosystems but also as guidance to entrepreneurs in building a supportive innovation ecosystem for their radical sustainability technologies. The term 'collective system building' describes processes and activities that networks of actors can strategically engage in to collectively build a favorable environment for their innovative sustainability technology. First, a strategy framework for collective system building is presented, which focuses on the processes and important activities for system building. The strategy framework consists of four key areas: technology development and optimization, market creation, socio-cultural changes and coordination. Each of these key strategic areas is composed of a set of system-building activities. This framework can be used as tool for strategy making by system-building ...