"The Flood Insurance and Mitigation Administration (FIMA), a component of the Federal Emergency Management Agency (FEMA), manages the National Flood Insurance Program (NFIP). … Nearly 20,000 communities across the United States and its territories participate in the NFIP by adopting and enforcing floodplain management ordinances to reduce future flood damage. In exchange, the NFIP makes Federally backed flood insurance available to homeowners, renters, and business owners in these communities. Community participation in the NFIP is voluntary."
Federal Emergency Management Agency: http://www.fema.gov