The Social Insurance Institution was established in 1934 by means of an Ordinance of the President of the Republic of Poland of 24 October 1934 on the amendment of the Act of 28 March 1933 on social insurance. At that time, five insurance institutions have been merged (Social Insurance Chamber, Sickness Insurance Institution, Accident Insurance Institution, White-Collar Employees' Insurance Institution, Blue-Collar Workers' Insurance Institution).

The Social Insurance Institution (ZUS) is the state organisational unit and holds legal personality. Its tasks are defined in the Act of 13 October 1998 on the social insurance system. ZUS also fulfils numerous functions entrusted by virtue of other laws.

The social insurance and health care systems reforms, which entered into force on 1 January 1999, and their structural nature, strengthened the position of the Social Insurance Institution as the main element of the administration of the Polish social security system.