Jurisdictions across Canada and around the world face the challenge of planning high-performing and sustainable health systems in response to growing healthcare demands. In this paper, we report on the process of developing principles for health system capacity planning by the Ministry of Health and Long-Term Care in Ontario. Integrating the results of a literature review on health system planning and a symposium with representatives from local health integration networks, we describe the following six principles in detail: (1) develop an aspirational vision, (2) establish clear leadership, (3) commit to stakeholder engagement, (4) engage patients and the public, (5) build analytics infrastructure and (6) revise policy when necessary.