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.