Due to the military hierarchy of medieval Europe, and the importance of the knight in the European Feudal system, professional soldiers were of great importance and social significance. The military equipment of the time was highly expensive, and high-quality wargear such as a mail hauberk represented a huge investment. Therefore a professional soldier who wore full metal gear to battle (including a helm and coif) was a representation of wealth and status. The more well equipped men a knight had in his retinue, the better his local standing. Due to the endemic in-fighting and civil disruptions of the 12th–14th Centuries, in the Hundred Years' War and across the borderlands of Scotland and Wales, military status was incredibly important, and could assure the survival of some families.
The next "step up" in the military hierarchy from the man-at-arms was the serjeant, a man of lesser rank and wealth to a knight, but with comparable equipment and training. Although the social structure of the Norman society of England was generally static, the easiest manner for a man to attain social rank and improve his standing was through military service, as the Norman states, unlike the Germanic ones, believed in knighting men of common birth who demonstrated nobility and courage on the field. Although this was rare, it was known, and therefore some men-at-arms would advance socially to the status of serjeants, and possibly knights if they performed a great notable deed and received reward. The knighting of squires and men-at-arms was sometimes done in an ignoble manner, simply to increase the number of knights within an army (such practice was common during the Hundred Year's War).
The term was used during the Hundred Years' War to refer to men not of the higher order, who fought either on horseback or on foot with swords and armour. A knight was technically a man-at-arms, but a man-at-arms was not a knight. In this way it was understood that a "man-at-arms" was a man of the higher echelon of the military scale, but neither of noble birth nor a knight himself. By this time, the term was only ever used to refer to professional soldiers, usually of a distinctly higher order than archers or Billmen and serving in roughly the same tactical role as knights, differing only in legal and social status. The term was phased out during the 16th century.
When used in allusion to a professional soldier in a regular army, the term is an honorary denotation and could be considered unusual usage.
In some countries, such as France, the men-at-arms (gens d'armes) became a paramilitary with police duties.
There, a military corps having such duties was first created in 1337 and was placed under the orders of the Constable of France (connétable), and therefore named connétablie. In 1626 after the abolition of the title of connétable, it was put under the command of the Maréchal of France, and renamed Maréchaussée. Its main mission was protecting the roads from highwaymen.
The gens d'armes were originally heavy cavalry in the king's household, the equivalent of the "Honourable Corps of Gentlemen at Arms". In 1720 the maréchaussée was subordinated to the gendarmerie; after the French Revolution the maréchaussée was abolished and the gendarmerie took over its duties in 1791.