As governments and development finance institutions scale up delivery of climate finance commitments, the question of how to measure and ensure additionality becomes increasingly important. This paper presents new methodological approaches for assessing the additionality of climate investments, developed by Climate Policy initiative (CPI) through ongoing work monitoring and evaluating the Climate Public Private Partnership (CP3). CP3 is a GBP £130m program, funded by the UK’s International Climate Fund, which invests in climate-focused private equity (PE) funds in developing countries. It has dual commercial and development objectives, and aims to demonstrate to the market that climate investment is feasible and profitable.