Symposium D, “Compound Semiconductors for Energy Applications and Environmental Sustainability,” was held at the 2011 MRS Spring Meeting April 25-29 in San Francisco, California. Compound semiconductors have long been an integral part of everyday life. Many of these semiconductors exhibit direct band gaps that are tailorable over a wide range of energy. This property can be leveraged for many energy-related applications such as efficient lighting, high-efficiency solar cells, and efficient switching. Recent progress on their potential as emitters, sensing devices in biological and chemical environments, and high-efficiency power devices demonstrates their impact on conservation of energy and environment, and on mitigation of climate change. This volume contains reports from internationally known experts on the state of compound semiconductor-based devices with applications to environmental conservation and energy use reduction, challenges associated with realization of such devices, and obstacles to their widespread use.