An affinity group is a small group of activists (usually from 5-20) who work together on direct action. It is a non-hierarchical group, usually made up of trusted friends and other like-minded people. It is a highly effective method of organization, as many actions may require a number of people working on it in different areas. Use of an affinity group also serves to keep information within the group (rather than, say, police infiltrators).

The use of affinity groups dates back to 19th century Spain, where they were called tertulias or grupos de afinidad by Spanish anarchists. They became popular again in the 1970s in the anti-nuclear movement in the United States. Today, the tool is used by many different activists: animal rights, environmental, anti-war, and anti-globalization, to name some examples.

A collection of affinity groups working together is called a cluster.

Quotes

• Noam Chomsky: "If you assume correctly that whatever group you are in is being penetrated by the FBI, when something serious is happening, you don’t do it in a meeting. You do it with some people you know and trust, an affinity group and then it doesn’t get penetrated. That’s one of the reasons why the FBI has never been able to figure out what’s going on in any of the popular movements." [1]