The following discusses commonly asked questions about the National Provider Identification Number (NPI) that physicians, to the extent they are covered by the Health Insurance Portability and Accountability Act of 1996 (HIPAA) or otherwise required to do so by health plans or others with which they contract, have been required to use effective May 23, 2007 (May 23, 2008 for small health plans). For more information on HIPAA, including determining covered entity status, see CMA ON-CALL document #4100, “HIPAA Overview/Enforcement.” For more information on the electronic transactions which will use national provider identifiers, see CMA ON-CALL document #4104,“HIPAA Electronic Transaction Rule.”