ABSTRACT This perspective paper proposes a new conceptual framework for bottom-up climate mitigation: the Fossil Free Zones (FFZs) framework. The aim of the framework is to facilitate grassroots, goal-driven climate action, and government policy at increasingly higher levels, with a view to ‘tipping’ social systems away from their reliance on fossil fuels. The paper outlines the framework and the theory of change on which it is predicated, after first introducing the historical precedent that inspired it – the system of Nuclear Weapon Free Zones. The FFZs framework offers two main advantages over other anti-fossil fuel initiatives – such as the Fossil Fuel Non-Proliferation Treaty Initiative – though it is intended and designed to complement these, not compete with them. First, the FFZs framework combines a unified and accessible discursive frame with a focus on practical decarbonising activities at multiple levels of governance. The discursive frame promotes the diffusion of anti-fossil fuel norms while the practical activities promote positive (reinforcing) social, technological, economic and other feedback effects. Second, the combined focus on supply and demand increases the political resilience of anti-fossil fuel initiatives in the face of fossil fuel price fluctuations, and promotes cooperation between producer regions and urban consumer centres. Key policy insights Anti-fossil fuel activism has become a global phenomenon, but fossil fuel production and combustion continue to rise, threatening climate objectives. A system of Fossil Free Zones is proposed to further mobilise grassroots and subnational action against fossil fuels, and build anti-fossil fuel norms. A Fossil Free Zone is a geographic area characterised by the absence of fossil fuel production and consumption, with intermediate statuses based on fuel types and activities, e.g. ‘coal supply free zone’. Motivated groups set zone-related goals and work toward them, cooperating with others and across different levels of government as necessary, and declare the zones they have achieved. Ultimately, Fossil Free Zones could become institutionalised at national and international level, as has occurred with Nuclear Weapon Free Zones. Fossil Free Zones combine discursive framing with practical decarbonising activities, and address fossil fuel production and consumption, improving on other anti-fossil fuel initiatives.