Governments increasingly use their purchasing power to promote environmental policy objectives. We [...]study the relationship between public municipal green-building procurement policies and diffusion of the US Green Building Council's LEED certification program. We find a strong link between public green building procurement plans and voluntary private adoption of the LEED standard. We also observe an increase in LEED professional accreditation in communities that adopt a green procurement policy. We suggest that public policy may spur private certification by resolving the coordination problem that arises among developers and local building professionals in the diffusion of a new certification program.