The authors would like to thank Jan Corfee-Morlot, Sara Fyson, Raundi Halvorson-Quevedo, Nicolina Lamhauge and Suzanne Steensen from the Development Co-operation Directorate, and Jane Ellis and Randy Caruso from the Environment Directorate of the Organisation for Economic Co-operation and Development (OECD) for their comments on earlier drafts and help in carrying out this work. The authors would also like to thank all interview respondents for their insights and time dedicated to this research, many of whom also provided valuable comments on earlier drafts of the paper. This report explores current understanding of what makes international climate finance effective - focusing on climate-related development finance. Its scope includes, but is not limited to, official development assistance (ODA). The research approach used is qualitative, and is based on a series of in-depth interviews.