This article explores the principles that should guide efforts to raise finance for climate action in developing countries. It explains that: (1) there is an important role for private finance, which would be facilitated by having pervasive and broadly uniform emissions pricing around the world; (2) public finance is warranted by a range of market – and policy – failures associated with climate change and its mitigation; (3) raising tax revenues may be preferable to borrowing as a means of raising public finance; (4) how much could or should be raised by the many specific proposals for finance for climate action in developing countries is often uncertain; (5) two sets of proposals do particularly well when judged against this analysis: (i) expanding the scale and scope of the Clean Development Mechanism (CDM) and (ii) expanding the use of international financial institutions’ balance sheets.