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 in Sweden
Social security in Sweden is one of the parts of the Swedish welfare system and consists of various social insurances handled by the National Agency for Social Insurance (Swedish; Försäkringskassan), and also welfare given out on a need basis by local municipalities. They are the main conduits for redistribution of approximately 48% of the Swedish GDP in the form of taxed income.