Medieval communes in the European Middle Ages had sworn allegiances of mutual defense (both physical defense and of traditional freedoms) among the citizens of a town or city. These took many forms and varied widely in organization and makeup.

Communes are first recorded in the late 11th and early 12th centuries, thereafter becoming a widespread phenomenon. They had greater development in central-northern Italy, where they became city-states based on partial democracy. At the same time in Germany they became free cities, independent from local nobility.

The English and French word "commune" (Italian: comune) appears in Latin records in various forms. They come from Medieval Latin communia, plural form of commune (that which is common, community, state), substantive noun from communis (common). Ultimately, the Proto-Indo-European root is *mey- (to change, exchange).

When autonomy was won through violent uprising and overthrow, the commune was often called conspiratio (a conspiracy) (Italian: cospirazione).

During the 10th century in several parts of Western Europe, peasants began to gravitate towards walled population centers, as advances in agriculture (the three-field system) resulted in greater productivity and intense competition. In central and northern Italy, and in Provence and Septimania, most of the old Roman cities had survived—even if grass grew in their streets—largely as administrative centers for a diocese or for the local representative of a distant kingly or imperial power. In the Low Countries, some new towns were founded upon long-distance trade, where the staple was the woolen cloth-making industry. The sites for these ab ovo towns, more often than not, were the fortified burghs of counts, bishops or territorial abbots. Such towns were also founded in the Rhineland. Other towns were simply market villages, local centers of exchange.

Such townspeople needed physical protection from lawless nobles and bandits, part of the motivation for gathering behind communal walls, but also strove to establish their liberties, the freedom to conduct and regulate their own affairs and security from arbitrary taxation and harassment from the bishop, abbot, or count in whose jurisdiction these obscure and ignoble social outsiders lay. This was a long process of struggling to obtain charters that guaranteed such basics as the right to hold a market. Such charters were often purchased at exorbitant rates, or granted, not by the local power, but by a king or by the emperor, who came to hope to enlist the towns as allies in order to centralize power.

The walled city provided protection from direct assault at the price of corporate interference on the pettiest levels, but once a townsman left the city walls, he (for women scarcely travelled) was at the mercy of often violent and lawless nobles in the countryside. Because much of medieval Europe lacked central authority to provide protection, each city had to provide its own protection for citizens - both inside the city walls, and outside. Thus towns formed communes which were a legal basis for turning the cities into self-governing corporations. In most cases the development of communes was connected with that of the cities. However, there were rural communes, notably in France and England, that formed to protect the common interests of villagers. At their heart, communes were sworn allegiances of mutual defense. When a commune formed, all participating members gathered and swore an oath in a public ceremony, promising to defend each other in times of trouble, and to maintain the peace within the city proper.

The commune movement started in the 10th century, with a few earlier ones like Forlì (possibly 889), and gained strength in the 11th century in northern Italy, which had the most urbanized population of Europe at the time. It then spread in the early 12th century to France, Germany, Spain and elsewhere. The English state was already very centralized, so the communal movement mainly manifested itself in parishes, craftsmen's and merchants' guilds and monasteries. State officialdom expanded in England and France from the 12th century onwards, while the Holy Roman Empire was ruled by communal coalitions of cities, knights, farmer republics, prince-bishops and the large domains of the imperial lords. In eastern Europe, the splintering of Kievan Rus' allowed the formation of veche communes like the Novgorod Republic (1136-1478) and the Pskov Republic (1348-1510).