Meeting the Paris Agreement goals will need a rapid acceleration of finance towards clean energy investments in emerging and developing economies. Blended finance is an important tool that can help mobilise commercial investment towards clean energy, whilst preserving scarce public resources for wider climate and development objectives. A systematic approach to the deployment of blended finance – that tailors instruments to the nature of underlying barriers to commercial investment, minimises concessionality, has a clear exit strategy, and is co-ordinated within a wider ecosystem of support and enabling measures – can help maximise its development impact and stimulate private sector development. This paper explores specific features of clean energy projects, and the wider transition, to draw lessons for donors, policymakers in beneficiary governments, and financial institutions on whether and how best to deploy blended finance in the sector. It revisits the OECD DAC's Blended Finance Principles, specifically Principle 2: designing blended finance to increase the mobilisation of commercial finance, and explores their applicability to clean energy. It also explores sector-specific considerations for the deployment of clean energy, setting out the considerations development practitioners can make to inform better decision-making on, and maximise the development impact of, blended finance interventions.