NPI is a 10-digit number assigned to health care providers that last for their entire career. The National Provider Identifier (NPI) is a new numeric identifier that is being assigned to physicians and other health care providers by the Centers for Medicare and Medicaid Services (CMS). Individuals or organizations can apply for NPIs through the CMS National Plan and Provider Enumeration System (NPPES). The NPI replaced the unique physician identification number (UPIN), which was discontinued in June of 2007. The Health Insurance Portability and Accountability Act (HIPAA) required that a 10-digit national provider identifier be given to all health care providers covered by HIPAA. The NPI must be used instead of legacy provider identifiers in the HIPAA standards transactions.
Why is it important to the healthcare industry?
The NPI is an Administrative Simplification mandate of HIPAA. CMS is taking steps to improve the electronic transactions in health care with the NPI. It will improve the efficiency and effectiveness of the health care industry by simplifying the administration of the health care system and enabling the efficient electric transmission of certain health information.
What is NPPES?
The CMS manages a free public directory called the National Plan and Provider Enumeration System (NPPES) NPI Registry with all NPI documents. Certain sections of the NPI record, including the name of the health care provider, practice addresses, specialties, and other related information, are made public.

NPPES NPI REGISTRY NPI LOOKUP
There are several websites available that will help you with NPI lookup. On these sites, you have simply put the NPI number of the physician and you can get details of them. If you know the name and address of the physician then also you can simply put that on these sites to know the NPI number and vice versa.
These are few sites above that will help you with free NPI lookup. You just have to fill in the details and you will get the NPI information that you were looking for.