Special government bonds to fund the transition to sustainability have proliferated. It is argued here that use-of-proceeds sovereign green bonds issued by an investment-grade country have no environmental impact, and fail to achieve other policy objectives. Performance-linked bonds contribute to policy commitment and accountability, but are hard to price and calibrate. Implementing effective environmental policies is the best way to mobilize sustainability financing. Many governments, especially in Europe, have issued sustainability bonds, with the general aim of contributing to the financing of the transition to a sustainable economy. Much is claimed for them, and the sums involved are large. Now that evidence from diverse country experience has accumulated, it is worth assessing how well these instruments in fact achieve policy objectives, and thinking again about their optimal design. […]