Military volunteer in the context of "Internal Troops of Russia"

The Macedonian-Adrianopolitan Volunteer Corps (Bulgarian: Македоно-одринско опълчение, romanized: Makedono-odrinsko opalchenie, Macedonian: Македонско-одрински доброволни чети, romanized: Makedonsko-Odrinski dobrovolni četi; MAVC) was a volunteer corps of the Bulgarian Army during the Balkan Wars. It was formed on 23 September 1912 and consisted of Bulgarian volunteers from Macedonia and Thrace, regions still under Ottoman rule, and thus not subject to Bulgarian military service. Foreign volunteers were also welcome to join.

Freikorps (German: [ˈfʁaɪˌkoːɐ̯], "Free Corps" or "Volunteer Corps") were irregular German and other European paramilitary volunteer units that existed from the 18th to the early 20th centuries. They effectively served as mercenaries or private military companies, regardless of their own nationality. In German-speaking countries, the first so-called Freikorps ("free regiments", Freie Regimenter) were formed in the 18th century from native volunteers, enemy renegades, and deserters. These sometimes exotically equipped units served as infantry and cavalry (or, more rarely, as artillery); sometimes in just company strength and sometimes in formations of up to several thousand strong. There were also various mixed formations or legions. The Prussian von Kleist Freikorps included infantry, jäger, dragoons and hussars. The French Volontaires de Saxe combined uhlans and dragoons.

In the aftermath of World War I and during the German Revolution of 1918–19, Freikorps, consisting partially of World War I veterans, were raised as paramilitary militias. They were ostensibly mustered to fight on behalf of the government against the German communists attempting to overthrow the Weimar Republic. However, many Freikorps also largely despised the Republic and were involved in assassinations of its supporters, later aiding the Nazis in their rise to power.

Auxiliaries are support personnel that assist the military or police but are organised differently from regular forces. Auxiliary may be military volunteers undertaking support functions or performing certain duties such as garrison troops, usually on a part-time basis. Unlike a military reserve force, an auxiliary force does not necessarily have the same degree of training or ranking structure as regular soldiers, and it may or may not be integrated into a fighting force. Some auxiliaries, however, are militias composed of former active duty military personnel and have better training and combat experience than their regular counterparts.

The designation "auxiliary" has also been given to foreign or allied troops in the service of a nation at war. The term originated with the Latin eponymous Auxilia relating to non-citizen infantry and cavalry serving as regular units of the Roman Empire. In the context of colonial troops, locally recruited irregulars were often described as auxiliaries.

United States Volunteers (also called U.S. Volunteers, U.S. Volunteer Army, among other variations) were military volunteers called upon during wartime to help the United States Army. They were separate from the Regular Army and the militia.

Until the Militia Act of 1903, the land forces of the United States were divided into three organizations:

The Second Australian Imperial Force (2nd AIF, or Second AIF) was the volunteer expeditionary force of the Australian Army in the Second World War. It was formed following the declaration of war on Nazi Germany, with an initial strength of one infantry division and related auxiliary components. After considerable expansion of this force, three divisions were sent to the Middle East and North Africa, while the 8th Division was sent to garrison British Malaya and Singapore.

Under the Defence Act 1903, neither the part-time Militia nor the full-time Permanent Military Force (PMF) could serve outside Australia or its territories unless they volunteered to do so. The Second AIF fought against Nazi Germany, Italy, Vichy France and Japan. After the war, Australia's wartime military structures were demobilised and the 2nd AIF was disbanded, although a small cadre of its personnel became part of the Interim Army that was established in 1947, and from which the Australian Regular Army was formed in 1948.