This research studies business alliances that seek to address climate change, offering empirical evidence to address claims advanced by alliance supporters and critics. We collect a unique database of eleven major alliances (largely focused on financial service firms) and 424 major publicly-traded financial institutions, some of which became members of these alliances. We use diff-in-diff approaches to identify the effect of alliance membership and other empirical methods to study network, peer, and ““booster”“ effects. We find that financial service firms that join climate alliances show increased adoption of climate-aligned management practices; are more likely to adopt emissions targets, but not more ambitious targets; and show modest evidence of emissions reductions. The evidence shows no systematic markers of traditional anti-trust violations in the form of market pricing or concentration, nor any violations of fiduciary duty in the form of reduced risk-adjusted shareholder returns. Participation in multiple alliances (a ““booster effect”“), as well as peer and network effects, are correlated with increased adoption of practices and targets.