Freedom of association encompasses both an individual's right to join or leave groups voluntarily, the right of the group to take collective action to pursue the interests of its members, and the right of an association to accept or decline membership based on certain criteria. It can be described as the right of a person coming together with other individuals to collectively express, promote, pursue and/or defend common interests.

Freedom of association is both an individual right and a collective right, guaranteed by all modern and democratic legal systems, including the United States Bill of Rights, article 11 of the European Convention on Human Rights, section 2 of the Canadian Charter of Rights and Freedoms, and international law, including articles 20 and 23 of the Universal Declaration of Human Rights and article 22 of International Covenant on Civil and Political Rights. The Declaration on Fundamental Principles and Rights at Work by the International Labour Organization also ensures these rights.

Freedom of association is manifested through the right to join a trade union, to engage in free speech or to participate in debating societies, political parties, or any other club or association, including religious denominations and organizations, fraternities, and sport clubs and not to be compelled to belong to an association. It is closely linked with freedom of assembly, particularly under the U.S. Bill of Rights. Freedom of assembly is typically associated with political contexts. However, (e.g. the U.S. Constitution, human rights instruments, etc.) the right to freedom of association may include the right to freedom of assembly.

The courts and delegated officers of local jurisdictions may impose restrictions on any of the rights of a convicted criminal as a condition of a legal stipulation. Rights to freedom of association and freedom of assembly are waived under certain circumstances, such as a guilty plea or conviction, restraining orders and probationer's search and seizure procedures. Freedom of association is also legally restricted in certain circumstances such as with the Civil Rights Act, in which private discrimination against certain protected classes was made illegal.

The general freedom to associate with groups according to the choice of the individual, and for the groups to take action to promote their interests, has been a necessary feature of every democratic society. Because freedom of association necessarily recognizes pluralistic sources of power and organisation, aside from the government, it has been a primary target for repression by all dictatorial societies. In the United Kingdom, all forms of "combination" were prohibited and criminal, particularly worker organisations, until the Combination Act 1825. After this, it was still not by the Companies Act 1856, the Trade Union Act 1871 and the Criminal Conspiracy and Protection of Property Act 1875 that companies and then trade unions became generally lawful. In Germany, a similar set of repressive laws was put in place against both trade unions and social democrat organisations by the Bismarck government under the Sozialistengesetze (the "Socialist Acts") in 1878. These remained in force until 1890. In 1933, trade unions were once again prohibited by the Fascist dictatorship of Hitler's National Socialist party, and the existing unions were nationalized and combined into a single government controlled German Labor Front. In West Germany after World War II, free trade unions were quickly resurrected and guaranteed by the German Grundgesetz. In the United States, trade unions were classified by various state courts, at various times, as being in restraint of trade. Under the Clayton Act of 1914, trade unions were given a general freedom to organize and to act collectively to secure collective agreements, however further hurdles were put in place until the National Labor Relations Act of 1935 created a comprehensive labor code.

Freedom of association is enshrined by Universal Declaration of Human Rights in Article 20:

1. Everyone has the right to freedom of peaceful assembly and association.

2. No one may be compelled to belong to an association.