Policies to reduce greenhouse gas emissions can be categorized as demand-side measures, which reduce the consumption of fossil fuels, or supply-side measures,  which reduce fossil fuel extraction. Most governments have relied primarily on demand-side approaches to emissions reductions while largely eschewing supply-side policies, even though policy commitments thus far remain insufficient to limit global temperature rise to 1.5°C. The focus on demand-side policies may stem from a common perception by policymakers and economists that supply-side policies are vulnerable to emissions “leakage”—in which reduced domestic fossil fuel production (and hence emissions) is simply offset by increased production and emissions elsewhere—to which demand-side policies are supposedly immune. This paper shows that leakage is a concern for both supply- and demand-side policies alike when pursued on their own, as is commonly done. However, when supply- and demand-side policies are pursued in parallel with similar vigor, leakage can be mitigated or even eliminated. As a result, supply- and demand-side policies are  complementary in their goals of reducing greenhouse gas emissions. Far from being rivals, these two kinds of policies can be partners.