The world faces multiple critical and intertwined challenges: expanding electricity generation to meet the needs of growing economies and to supply power to the more than one billion people who currently lack access while reducing greenhouse gas emissions to nearly zero by 2050 – all while maintaining the integrity of our world's ecosystems, including conserving the planet's remaining free-flowing rivers. This report describes how the world can tackle these intertwined challenges and support global efforts to achieve the Sustainable Development Goals (SDGs) and the targets under the Paris Agreement, by moving rapidly toward electricity systems that are low carbon, low cost, and low impact (Introduction).