Renewable sources of energy now stand poised to lead the world in new electricity supply. Supported by policies aimed at enhancing energy security and sustainability, renewable power expanded at its fastest rate to date in 2014 and now represents more than 45% of overall supply additions. Deployment continues to shift towards energy-hungry emerging markets, and some countries, such as China and India, have bolstered ambitions. Moreover, sustained technology progress, expansion into newer markets with better resources, and improved financing conditions are facilitating more cost-effective deployment for the most dynamic technologies (solar photovoltaics and onshore wind). But will renewable growth in the coming years falter, or could an even faster expansion take place? Dramatic falls in fossil fuel prices over the past year have raised questions over the competitiveness of renewables and government willingness to maintain policy support. Policy uncertainties remain in the Organisation for Economic Co-operation and Development (OECD), where electricity demand has been stagnating in some markets and the rapid deployment of renewables can put incumbent utilities under pressure. For emerging markets, regulatory, grid and financing conditions can pose challenges to growth. Meanwhile, progress in the transport and heating sectors remains comparably slow, with advanced biofuels and renewable heat technologies requiring enhanced policy attention to scale up. The Medium-Term Renewable Energy Market Report 2015 assesses these trends in the electricity, transport and heat sectors, identifying drivers and challenges to deployment, and making projections through 2020. It also assesses the potential impacts of enhanced policy actions under an accelerated case for renewable power, which would put the world more firmly on a path to a more sustainable and secure energy system.