Hydraulic fracturing, or “fracking” extracts oil and gas from unconventional sources. This has changed the landscape of fossil fuel exploration and production, has greatly increased the world’s reserves of oil and gas, and played a major role in reducing the cost of a barrel of oil. The extraction process is controversial and several jurisdictions have banned it because of environmental and human health concerns. I will review the basic geology of fracking, discuss the controversial issues around the process and tie it into our present concerns about global warming.