Implementation for the National Provider Identifier (NPI) begins May 23, 2005. This identifier is a requirement of the Health Insurance Portability and Accountability Act (HIPAA) and must be used by health care providers including clinical social workers, health plans, health care clearinghouses, and other covered entities that conduct electronic transactions. The compliance date is May 23, 2007. Small health plans have until May 23, 2008 to comply.