A militia generally is an army or other fighting unit that is composed of non-professional fighters, citizens of a nation or subjects of a state or government who can be called upon to enter a combat situation, as opposed to a professional force of regular, full-time military personnel, or historically, members of the fighting nobility class (e.g., knights or samurai). Unable to hold their own against properly-trained and -equipped professional forces, it is common for militias to engage in guerrilla warfare or defense instead of being used in open attacks and offensive actions.

Militsiya or militia (, , , , , , , , , , ), often confused with militia, is used as an official name of the civilian police in several former communist states. The term was used in the Soviet Union and several Warsaw Pact countries, as well as in the non-aligned SFR Yugoslavia, and it is still commonly used in some of the individual former Soviet republics and eastern Europe.