Exposure of non-smokers and smokers to second-hand tobacco smoke causes cancer, heart disease, lung disease, and childhood illness including cot death and asthma. Worldwide, 600 000 people are estimated to die annually as a result of exposure to second-hand smoke (SHS). Despite international commitments to eliminate exposure to tobacco smoke, only 11 per cent of the world’s population is adequately protected by law from exposure to second-hand smoke. This represents an unacceptable gap between commitment and practice. Action by cities can help close this gap. While national laws that protect all of a country’s residents from exposure are ideal, the reality is that cities can often pass legislation sooner than countries, and opposition from tobacco companies can usually be more successfully overcome at local rather than national level. City leaders, as credible voices for their citizens, can also directly advocate for smoke-free laws at national level.