We examine whether corporate green bond issuance improves firm-level environmental performance. Using a global sample of listed firms (2013-2022) and a staggered difference-in-differences design, we compare issuers to matched non-issuers using direct environmental metrics: waste, water pollutants, and composite emissions intensity (CEI). We find significant reductions in all three measures post-issuance, with effects strengthening over time. These improvements are facilitated by increased environmental innovation and are more pronounced among firms with weaker governance and in countries with less stringent regulation. Our results suggest green bonds can generate real environmental benefits, particularly where institutional monitoring is otherwise lacking.