Policy diffusion is a process whereby political bodies 'learn' policy solutions to public health problems by imitating policy from similar jurisdictions. This suggests that diffusion is a critical element in the policy development process, and that its role must be recognised in any examination of policy development. Yet, to date, no systematic work on the diffusion of smoke-free spaces bylaws has been reported. We examined the diffusion of municipal smoke-free bylaws over a 30-year period in the provinces of Alberta and Ontario, Canada, to begin to address this gap and to determine whether spatial patterns could be identified to help explain the nature of policy development. Bylaw adoption and change were analysed within local, regional, and provincial contexts. Geographical models of hierarchical and expansion diffusion in conjunction with the diffusion of innovations framework conceptually guided the analyses. Study findings contribute to a broader understanding of how and why health policies diffuse across time and place. Policy development can be a powerful mechanism for creating environments that support healthy decisions; hence, an understanding of policy diffusion is critical for those interested in policy interventions aimed at improving population health in any jurisdiction.