Development of shale gas and tight oil, or unconventional oil and gas (UOG), has dramatically increased domestic energy production in the U.S. UOG resources are typically developed through the use of hydraulic fracturing, which creates high-permeability flow paths into large volumes of tight rocks to provide a means for hydrocarbons to move to a wellbore. This process uses significant volumes of water, sand, and chemicals, raising concerns about risks to the environment and to human health. Researchers in various disciplines have been working to make UOG development more efficient, and to better understand the risks to air quality, water quality, landscapes, human health, and ecosystems. Risks to air include releases of methane, carbon dioxide, volatile organic compounds, and particulate matter. Water-resource risks include excessive withdrawals, stray gas in drinking-water aquifers, and surface spills of fluids or chemicals. Landscapes can be significantly altered by the infrastructure installed to support large drilling platforms and associated equipment. Exposure routes, fate and transport, and toxicology of chemicals used in the hydraulic fracturing process are poorly understood, as are the potential effects on terrestrial and aquatic ecosystems and human health. This is made all the more difficult by an adaptable and evolving industry that frequently changes methods and constantly introduces new chemicals. Geoscientists responding to questions about the risks of UOG should refer to recent, rigorous scientific research.