A policy paper for CGD. Is research into a Covid-19 vaccine a suitable use of Official Development Assistance (ODA)? What about finance to reduce carbon dioxide emissions? Both are clearly good ways to spend money with considerable benefits to developing countries, but is that enough? This note attempts to tease apart a discussion of “is this ODA” from “is this a global public good?” and then separate out again “is this ODA and/or a global public good?” from “is this an efficient way to spend money?” It uses that discussion to frame conclusions about how and what financing of GPGs should be counted as ODA and takes a specific look at the issue of climate change in that regard.