From the Dust Bowl of the 1930s to extreme water shortages in California in recent years, modern societies often take water’s abundance for granted until it becomes scarce. One of many problems climate change may exacerbate, drought is a complex phenomenon at the intersection of a range of scientific disciplines and public policy issues. Benjamin I. Cook, adjunct associate research scientist at Lamont-Doherty Earth Observatory, brings together climate science, hydrology and ecology to provide an overview of drought and its environmental and social consequences. He explains the global water cycle, the distribution of water resources, Earth’s climate system and discusses drought variability over time. He also considers the socioeconomic impacts of drought and the role of drought risk-management policy, especially in light of climate change.