In the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, a Social Security number (SSN) is a nine-digit number issued to U.S. citizens

United States nationality law

Article I, section 8, clause 4 of the United States Constitution expressly gives the United States Congress the power to establish a uniform rule of naturalization. The Immigration and Naturalization Act sets forth the legal requirements for the acquisition of, and divestiture from, citizenship of...

, permanent residents, and temporary (working) residents under section 205(c)(2) of the Social Security Act, codified as . The number is issued to an individual by the Social Security Administration

Social Security Administration

The United States Social Security Administration is an independent agency of the United States federal government that administers Social Security, a social insurance program consisting of retirement, disability, and survivors' benefits...

, an independent agency of the United States government

Independent agencies of the United States government

Independent agencies of the United States federal government are those agencies that exist outside of the federal executive departments...

. Its primary purpose is to track individuals for taxation

Taxation in the United States

The United States is a federal republic with autonomous state and local governments. Taxes are imposed in the United States at each of these levels. These include taxes on income, property, sales, imports, payroll, estates and gifts, as well as various fees.Taxes are imposed on net income of...

 purposes.

A Social Security number may be obtained by applying on Form SS-5, "Application for A Social Security Number Card".
The SSNs were issued by the Social Security Administration in November 1935 as part of the New Deal

New Deal

The New Deal was a series of economic programs implemented in the United States between 1933 and 1936. They were passed by the U.S. Congress during the first term of President Franklin D. Roosevelt. The programs were Roosevelt's responses to the Great Depression, and focused on what historians call...

 Social Security program.