Chasseur (/ʃæˈsɜːr/ shass-UR, French: [ʃasœʁ] ^ⓘ), a French term for "hunter", is the designation given to certain regiments of French and Belgian light infantry (chasseurs à pied) or light cavalry (chasseurs à cheval) to denote troops trained for rapid action.

This branch of the French Army originated during the War of the Austrian Succession when, in 1743, Jean Chrétien Fischer was authorized by the Marshal de Belle-Isle to raise a 600 strong mixed force of infantry and cavalry. It was called Chasseurs de Fischer. During the remainder of the 18th century various types of light troops (troupes légères) were employed within the French army, either as independent units or as companies within existing regiments. In 1788, there were 8 battalions of chasseurs, and in March 1793 this was expanded to 21 battalions. The first battalions of Chasseurs raised by 1788 included:

The chasseurs à pied were the light infantrymen of the French Imperial army. They were armed the same as their counterparts in the regular line infantry (fusilier) battalions, but were trained to excel in marksmanship and in executing manoeuvres at high speed. From 1840, they wore a long-skirted frock coat. After 1850, however the chasseurs adopted a uniform consisting of a short frock coat with slits in the sides on the bottom edge to allow for better freedom of movement than the previous design. They also wore light blue baggy trousers (in contrast to the red of the line infantry) tucked into jambières (leather gaiters). The other light infantry unit type, the voltigeurs, specialised as skirmishers, and for advance screening of the main force. The chasseurs could also be called upon to form advance guards and scouting parties alongside the voltigeurs.

Following the Napoleonic Wars the chasseurs à pied continued to exist as a separate corps within the infantry. Initially a specially trained elite, their tactical role eventually came to match that of the ordinary lignards (line infantry). By the late 19th century the differences between the two branches were confined to uniform and insignia, although the chasseurs retained a strong esprit de corps. Immediately after the Franco-Prussian War it was argued that the continued existence of a nominally elite class of infantry that was in fact armed and trained to the same standards as the ordinary soldier, was contrary to both military utility and the egalitarian principles of the new republic. However public opinion, influenced by the occasions on which the chasseurs had distinguished themselves during the war was opposed to the disbanding of this distinctive corps. Under the Third Republic the chasseurs à pied were increased from 20 to 30 battalions. Of these, 4 saw active service in Tunisia, one in Indochina, and one in Madagascar during the period 1880-1896. Twelve of the chasseur battalions were re-designated as mountain infantry (chasseurs alpins). The remaining chasseur battalions were deployed near the frontier with Germany as part of the troupes de couverture, charged with covering the bulk of the army during mobilization.

During World War I the French Army maintained 31 battalions of infantry chasseurs plus a varying number of reserve and territorial units. Each infantry division was expected to include at least one battalion of either chasseurs à pied or chasseurs alpine. Each battalion had an establishment of 1,300 to 1,500 men. They were reportedly nicknamed schwarze Teufel (black devils) by their German opponents, in reference to their dark colored uniforms. The chasseurs served mainly on the Western Front but detachments were sent to reinforce the Italian front in 1917.

The chasseurs à cheval, a type of French light cavalry, date from 1743 when an independent unit (Fischer's Volunteer Company of Chasseurs) was raised during the War of the Austrian Succession to counter Trenck's Pandurs and Croats employed as irregulars by the Austrian army. Originally a mixed corps of light infantry and horsemen, this force proved sufficiently effective to warrant the creation of a single corps: Dragoons-chasseurs de Conflans. In 1776 this and other volunteer "legions" had their mounted elements converted into 24 squadrons of chasseurs à cheval, each of which was attached to one of the existing dragoon regiments of the royal cavalry. In 1779 these squadrons were amalgamated into six regiments, each of which was given a regional title (1st Chasseurs des Alpes, 2nd Chasseurs des Pyrenees, etc.). In 1788, 6 dragoon regiments were converted to chasseurs à cheval and during the period of the Revolutionary Wars the number was again increased, to 25.

During their earlier history these regiments lacked the higher profile of the identically-armed (but much more lavishly uniformed) hussars. Distinguished by dark green uniforms and a bugle-horn badge, they were frequently used as advance scouting units providing valuable information on enemy movements. Both Napoleon's Imperial Guard and the Royal Guard of the Restoration each included a regiment of chasseurs à cheval. In addition Napoleon added a further 5 line regiments to those inherited from the Revolutionary period. At the beginning of the Franco-Prussian War of 1870, the French Army had 12 regiments of chasseurs à cheval, grouped with 8 hussar regiments to form the light branch of the cavalry and tasked with primarily reconnaissance duties. This intended role continued through World War I and the chasseurs à cheval remained entirely horse mounted until the 1^er RCh was motorised in June 1940. Disbanded after the Battle of France, these units were reconstituted in 1944–45 as light armor.

During the French occupation of Algeria, regiments of chasseurs d'Afrique were raised. These were light cavalry recruited originally from French volunteers and subsequently from the French settlers in North Africa doing their military service. As such they were the mounted equivalent of the zouaves.