Leaderless resistance is a social "resistance" strategy in which small, independent groups or individuals challenge an established institution, such as a law, economic system, social order, government, et cetera. Leaderless resistance can encompass anything from non-violent protests and consumer boycotts to civil disobedience, vandalism, and violence. Leaderless cells lack bidirectional, vertical command links and operate without hierarchical command. While it lacks a central command, the concept includes a common goal between the individual actor and the group or social movement from which the ideology was learned. The name "leaderless resistance" may be seen as partly misleading as there may actually be very influential individuals within the movement who may encourage (but not order) others to take actions.
The term itself derives from Ulius Louis Amoss who was a US intelligence officer who wrote an essay titled "Leaderless Resistance" in the 1950s after he retired. Amoss was upset with what he wrote was bad operational practices of the CIA regarding how to handle and encourage resistance movements in Communist areas. However, the concept in practice exited before this.
"Leaderless resistance" strategies have been employed by a wide range of movements and groups. Many movements/groups have encouraged non-organized supporters to do legal actions, such as non-violent protests and boycotts. There may also be pro-establishment activism by individuals not formally part of any organizations, such as some forms of hasbara, but then the term "resistance" (against an established institution) is inappropriate.
There are also illegal/violent actions not controlled by a central command that supporters may consider to be "resistance". Various Islamist terrorist organizations such as Al-Qaeda may consist of groups largely acting on their own. A prominent example is various anarchist organizations that reject strong leadership and hierarchies not just as a tactic, but as a fundamental part of their ideology. Anarchist terrorism has a long history that has included killing several heads of state, such as US President William McKinley. Various often far left influenced movements, such as animal rights activists and radical environmentalists, may also use such tactics. Another example is various violent "anti-racist" organizations such as Antifa.
Some nationalist organizations/individuals have advocated some form of "leaderless resistance" including Troy Southgate (during his time as a leading activist in the National Revolutionary Faction and a pioneer of National-Anarchism), Combat 18, and Louis Beam (who also wrote an essay titled "Leaderless Resistance"). However, most nationalist organizations have been more or less hierarchical. Also, anarchist ideologies have been much less influential than in the far left. Some forms of internet activism may possibly be considered to be forms of "leaderless resistance".