There is plenty of knowledge on why we need to act on climate change, and what we should and could do. However, knowledge on what mitigation actually costs is rather limited, especially from the perspective of climate finance providers on a country by country basis. There are several studies that estimate global investment requirements, for example EIA (2012), McKinsey (2009) and the UNFCCC (2008); however, none really tell you how much finance would actually be required from public international climate finance purses to achieve global mitigation goals, and how this should best be delivered. This policy update provides a brief overview of climate finance needs from both a societal and project developer’s perspective, what we currently know about developing countries’ finance needs, and the most suitable financial instruments.