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 when five insurance institutions (Social Insurance Chamber, Sickness Insur­ance Institution, Accident Insurance Institution, White-Collar Employees’ Insurance Institution, Blue-Collar Workers’ Insurance Institution) merged into one.

The Social Insurance Institution is a state organisational unit with legal personality. Its tasks are defined in the Act of 13 October 1998 on the social insurance system. ZUS also performs many other tasks assigned to it under other laws.

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