A National Provider Identifier (NPI) is a 10-digit number required on all HIPAA standard electronic transactions. It is a unique identification number for covered health care providers, created to improve the efficiency and effectiveness of electronic transmission of health information. A sole proprietor/sole proprietorship is an individual and is eligible for a single NPI. The sole proprietor must apply for the NPI using his or her own Social Security Number (SSN), not an Employer Identification Number (EIN) even if he/she has an EIN. Because a sole proprietor/sole proprietorship is an individual, he/she cannot be a subpart and cannot designate subparts. A sole proprietor is eligible for only one NPI, just like any other individual.