A free company (sometimes called a great company or, in French, grande compagnie) was an army of mercenaries between the 12th and 14th centuries recruited by private employers during wars. They acted independently of any government, and were thus "free". They regularly made a living by plunder when they were not employed; in France they were called routiers and écorcheurs and operated outside the highly structured law of arms. The term "free company" is most often applied to those companies of soldiers which formed after the Peace of Brétigny during the Hundred Years' War and were active mainly in France, but it has been applied to other companies, such as the Catalan Company and companies that operated elsewhere, such as in Italy and the Holy Roman Empire.

The free companies, or companies of adventure, have been cited as a factor as strong as plague or famine in the reduction of Siena from a glorious rival of Florence to a second-rate power during the later 14th century; Siena spent 291,379 florins between 1342 and 1399 buying off the free companies. The White Company of John Hawkwood was active in Italy in the latter half of the 14th century.

Mercenary groups first appeared in the 12th century, when they participated in the Anarchy (a conflict of succession between King Stephen and Empress Matilda between 1137 and 1153).

In the 1180s, similar groups were integrated into the armies of the King of France under Philip II of France. These troops of seasoned mercenaries were organized and mobile, a valuable advantage during the battles of the time, and were important elements of the armies of Henry II of England and his son, Richard I. King John used them at the beginning of his reign, when he was richer and more powerful than the King of France. However, in 1204, he did not pay the mercenaries. Philip II of France used them to overcome the Plantagenets.

During the Hundred Years War between England and France there were intermittent hostilities punctuated by periods of truce, when soldiers would be laid off en masse. In the absence of civilian skills and opportunities many, especially the foreign soldiers, formed armed bands known as bandes de routiers or écorcheurs and made a living by pillaging the countryside of southern France until hostilities resumed. Similar events occurred in Spain and Germany. By the time of the Treaty of Brétigny (1360), which brought about a several years suspension of the Hundred Years War, the bands had grown in size to the point where they had evolved an internal structure and adopted romantic names. The Tards-Venus (late-comers), led by Seguin de Badefol, ravaged Burgundy and Languedoc and even defeated the forces of the Kingdom of France at the Battle of Brignais in 1362.

The Catalan Company, formed in Spain in the early 1300s, fought in the Byzantine Empire before ending up in what is now Greece and the Navarrese Company, also formed in Spain, followed them there.

By 1356, free companies, men at arms, and brigands had spread throughout the country from the Seine to the Loire engaging in unlawful activities. They had especially infested the roads from Paris to Orléans, Chartres, Vendôme, and Montargis.

Brigands were recruited from all nations, but mainly from troops dismissed from the army of Edward III of England after the peace treaty of Brétigny. On October 24, 1360, after the Treaty of Calais ratified the ceasefire of 8 May, Edward III had ordered the evacuation of English troops from fortresses in many parts of France.