During the Middle Ages, the Kingdom of France was a decentralised, feudal monarchy. In Brittany, Normandy, Lorraine, Provence, East Burgundy and Catalonia (the latter now a part of Spain), as well as Aquitaine, the authority of the French king was barely felt. France in the Middle Ages (roughly, from the 10th century to the middle of the 15th century) was marked by the fragmentation of the Carolingian Empire and West Francia (843–987); the expansion of royal control by the House of Capet (987–1328), including their struggles with the virtually independent principalities (duchies and counties, such as the Norman and Angevin regions), and the creation and extension of administrative and state control (notably under Philip II Augustus and Louis IX) in the 13th century; and the rise of the House of Valois (1328–1589), including the protracted dynastic crisis against the House of Plantagenet and their Angevin Empire, culminating in the Hundred Years' War (1337–1453) (compounded by the catastrophic Black Death in 1348), which laid the seeds for a more centralised and expanded state in the early modern period and the creation of a sense of French identity.

Up to the 12th century, the territory experienced an elaboration and extension of the seigneurial economic system (including the attachment of peasants to the land through serfdom); the extension of the feudal system of political rights and obligations between lords and vassals; the so-called "feudal revolution" of the 11th century during which ever smaller lords took control of local lands in many regions; and the appropriation by regional/local seigneurs of various administrative, fiscal and judicial rights for themselves. From the 13th century on, the state slowly regained control of a number of these lost powers. The crises of the 13th and 14th centuries led to the convening of an advisory assembly, the Estates General, and also to an effective end to serfdom. During the 70-year reign of Louis XIV, absolutist policies from Paris tightly constrained the regional nobility, centralising political power at Versailles.

From the 12th and 13th centuries on, France was at the centre of a vibrant cultural production that extended across much of western Europe, including the transition from Romanesque architecture to Gothic architecture and Gothic art; the foundation of medieval universities (such as the universities of Paris (recognised in 1150), Montpellier (1220), Toulouse (1229), and Orleans (1235)) and the so-called "Renaissance of the 12th century"; a growing body of secular vernacular literature (including the chanson de geste, chivalric romance, troubadour and trouvère poetry, etc.) and medieval music (such as the flowering of the Notre Dame school of polyphony).

From the Middle Ages onward, French rulers believed their kingdoms had natural borders: the Pyrenees, the Alps and the Rhine. This belief was used as a pretext for an aggressive policy and repeated invasions. However, not all of these territories were part of the kingdom, and the authority of the king within his kingdom was quite fluctuant. The lands that composed the Kingdom of France showed great geographical diversity; the northern and central parts enjoyed a temperate climate while the southern part was closer to the Mediterranean climate. While there were great differences between the northern and southern parts of the kingdom, there were equally important differences depending on the distance of mountains: mainly the Alps, the Pyrenees and the Massif Central. France had important rivers that were used as waterways: the Loire, the Rhône, the Seine as well as the Garonne. These rivers were settled earlier than the rest, and important cities were founded on their banks, but they were separated by large forests, marsh, and other rough terrains.

Before the Romans conquered Gaul, the Gauls lived in villages organised in wider tribes. The Romans referred to the smallest of these groups as pagi and the widest ones as civitates. These pagi and civitates were often taken as a basis for the imperial administration and would survive up to the Middle Ages when their capitals became centres of bishoprics. These religious provinces would survive until the French Revolution. Southern Gaul was more heavily populated, and therefore more episcopal sees were present there at first while in northern France they shrank greatly in size because of the barbarian invasions and became heavily fortified to resist the invaders.

Discussion of the size of France in the Middle Ages is complicated by distinctions between lands personally held by the king (the "domaine royal") and lands held in homage by another lord. The notion of res publica inherited from the Roman province of Gaul was not fully maintained by the Frankish kingdom and the Carolingian Empire; by the early years of the Direct Capetians, the French kingdom was more or less a fiction. The "domaine royal" of the Capetians was limited to the regions around Paris, Bourges and Sens. The great majority of French territory was part of Aquitaine, the Duchy of Normandy, the Duchy of Brittany, the Comté of Champagne, the Duchy of Burgundy, the County of Flanders and other territories. In principle, the lords of these lands owed homage to the French king for their possession, but in reality the king in Paris had little control over these lands, and this was to be confounded by the uniting of Normandy, Aquitaine and England under the Plantagenet dynasty in the 12th century.

Philip II Augustus undertook a massive French expansion in the 13th century, but most of these acquisitions were lost both by the royal system of "apanage" (the giving of regions to members of the royal family to be administered) and through losses in the Hundred Years' War. Only in the 15th century would Charles VII and Louis XI gain control of most of modern-day France (except for Brittany, Navarre, and parts of eastern and northern France).

The weather in France and Europe in the Middle Ages was significantly milder than during the periods preceding or following it. Historians refer to this as the "Medieval Warm Period", lasting from about the 10th century to about the 14th century. Part of the French population growth in this period is directly linked to this temperate weather and its effect on crops and livestock. The vast majority of the population—between 80 and 90 percent—were peasants.