National Insurance number
The National Insurance number is used as a reference number in the Pay As You Earn system, and also by the self-employed. It is also used in applications for Individual Savings Accounts (ISAs), to check that an individual has opened only one ISA in a tax year.
Social Security Institution
The Social Security Institution () is the governing authority of the Turkish social security system. It was established by the Social Security Institution Law No:5502, which was published in the Official Gazette No: 26173 on June 20, 2006. This brought five different retirement systems that affected civil servants, contractual paid workers, agricultural paid workers, and self-employed workers into a single retirement system offering equal actuarial rights and obligations.