The future of renewable energy is fundamentally a choice, not a foregone conclusion given technology and economic trends. The new REN21 Renewables Global Futures Report illuminates that choice by showing the range of credible possibilities for the future of renewable energy. The report is not one scenario or viewpoint, but a synthesis of the contemporary thinking of many, as compiled from 170 interviews with leading experts from around the world, including CEOs and parliamentarians, and from 50 recently published energy scenarios by a range of organizations. Conservative projections show 15-20% global energy shares from renewables in the long-term to 2030 and 2050, about the same as the current share. High-renewables projections show shares in the 50-95% range. A range of integration options for electric power grids, buildings, industry, and transport are possible. Annual investment in renewable energy rose from $40 billion in 2004 to over $260 billion today, and several projections reach to $500 billion by 2020 and beyond. Strong future growth in national markets is projected from a range of policies and targets, with cases for the US, EU, Japan, China, and India, and further discussion of developing countries. Projections for global technology markets show cost reductions, technology evolution possibilities, and multi-fold capacity increases. A series of "Great Debates" throughout the report frame current issues.