This paper examines the effect of board gender diversity on firms' carbon emissions. Using a sample of firms from 43 countries during the 2005-2019 period, we establish that firms with more gender-diverse boards have a lower carbon footprint. Our results are shown to be robust for a battery of sensitivity checks, including the use of alternative definitions of board gender di-versity, multiple estimation methods, inclusion of additional control variables, and potential endogeneity concerns.