The Franks (Latin: Franci or gens Francorum; French: Francs) were a Germanic people who were first mentioned by name in 3rd-century Roman sources, living near the Lower Rhine, on the northern frontier of the Roman Empire. Later, Romanized Frankish dynasties based within the collapsing Western Roman Empire became the rulers of the whole region between the rivers Loire and Rhine. They subsequently imposed power over many other post-Roman kingdoms both inside and outside the old empire. Beginning with Charlemagne in 800, Frankish rulers were given recognition by the Catholic Church as successors to the old emperors.

Although the Frankish name does not appear until the 3rd century, at least some of the original Frankish tribes had long been known to the Romans under their own names, both as allies providing soldiers, and as enemies. The Germanic tribes who were called Franks in Late Antiquity are associated with the Weser-Rhine Germanic/Istvaeonic cultural-linguistic grouping. The Franks were first reported as working together to raid Roman territory. However, from the beginning, the Franks also suffered attacks upon them from outside their frontier area, by the Saxons, for example, and as frontier tribes they desired to move into Roman territory, with which they had centuries of close contact.

Frankish peoples inside Rome's frontier on the Rhine river are often divided into two groups - the Salian Franks who from their first appearance were permitted to live in Roman territory; and the Ripuarian or Rhineland Franks who, after many attempts, eventually conquered the Roman frontier city of Cologne and took control of the left bank of the Rhine. In the 450s and 460s, Childeric I, a Salian Frank, was one of several military leaders commanding Roman forces with various ethnic affiliations in Roman Gaul (roughly modern France). Childeric and his son Clovis I faced competition from the Roman Aegidius as competitor for the "kingship" of the Franks associated with the Roman Loire forces (according to Gregory of Tours, Aegidius held the kingship of the Franks for 8 years while Childeric was in exile). This new type of kingship, perhaps inspired by Alaric I, represents the start of the Merovingian dynasty which succeeded in conquering most of Gaul in the 6th century, as well as establishing its leadership over all the Frankish kingdoms on the Rhine frontier. It was on the basis of this Merovingian empire that the resurgent Carolingians eventually came to be seen as the new Emperors of Western Europe in 800.

The terms "Frank" or "Frankish" subsequently developed several different levels, sometimes representing a very large part of Europe, and on the other hand sometimes limited to France. In the High and Late Middle Ages, Western Europeans shared their allegiance to the Catholic Church and worked as allies in the Crusades beyond Europe in the Levant. In 1099, the crusader population of Jerusalem mostly comprised French settlers who, at the time, were still referred to as Franks, and other Europeans such as Spaniards, Germans, and Hungarians. French knights made up the bulk of the steady flow of reinforcements throughout the two-hundred-year span of the Crusades, in such a fashion that the Arabs uniformly continued to refer to the crusaders and West Europeans as Franjī caring little whether they really came from France. The French Crusaders also imported the French language into the Levant, making French the base of the lingua franca (lit. "Frankish language") of the Crusader states. This has had a lasting impact on names for Western Europeans in many languages. Western Europe is known alternatively as "Frangistan" to the Persians.

Following the Treaty of Verdun in 843, the Frankish Realm was divided into three separate kingdoms: West Francia, Middle Francia, and East Francia. In 870, Middle Francia was partitioned again, with most of its territory being divided among West and East Francia, which would hence form the nuclei of the future Kingdom of France and the Holy Roman Empire respectively, with West Francia (France) eventually retaining the choronym.