The Popular Latin was so firmly established in Gaul that the succeeding conquerors of the country, the German tribes, Visigoths, Bourguignons, and Franks, did not impose their language upon the conquered territory; instead they adopted the language that they found there. In modern French only about 400 words are of Germanic origin, for example, franc ("free") and français ("French"), both from the Germanic word Franko ("freeman"); fauteuil ("armchair") from the Germanic faldastol; and auberge ("inn"), from the Germanic heriberga. Greek words were also introduced into Popular Latin at various times, beginning in the 6th century, through Greek colonies along the Mediterranean Sea, notably those at Marseille and Nice. By the 7th century the language had been greatly modified by the people of France; the language spoken by them at that time was known as the Roman, or Romanic, language and was spoken by the upper classes as well as common people. As early as the 6th century, the homilies of the church councils that took place in France were translated into Romanic, and in the 8th century the Frankish leader Charlemagne by royal edict ordered church dignitaries to deliver their sermons in the popular tongue.

In early medieval times the spoken languages north and south of the Loire River began to develop separately. By the end of the 13th century they had become two distinct languages, the langue d'oïl of the north and the langue d'oc of the south; the terms were derived from oïl and oc, the words for "yes" in each of the languages. The chief phonetic difference in the two languages was their treatment of the free unaccented vowel a of Latin. The vowel became e in the langue d'oïl but remained unchanged in Provençal, the principal dialect of the langue d'oc; thus, the Latin word mare ("sea") became mer in the langue d'oïl and mar in Provençal. In each language several dialects developed. It seemed that the sothern tongue would establish supremacy over the langue d'oïl, but after the 12th century the langue d'oc rapidly became less important. The langue d'oc has contributed about 500 words to modern French, including bague ("ring"), cadeau ("gift"), and velours ("velvet"). The principal dialects of the langue d'oïl were named for the five northern provinces in which they were spoken: Île de France, Normandy, Picardy, Poitou, and Bourgogne. After the accession of Hugh Capet as king of France in 987, Paris became the seat of government, and the language spoken there began to dominate other French dialects, as the court at Paris became politically important to the provincial nobility. Modern French has developed directly from the dialect of the Île de France, which gradually superseded other French dialects during the late Middle Ages.

In the 12th and 13th centuries the langue d'oïl was popular throughout Europe. It was the court language of Naples; German princes and barons maintained French-born tutors who taught it to their children, and in England for the two centuries following the Norman Conquest in 1066, French strongly rivaled English as the spoken language of the land and almost supplanted it as the literary language. See Norman French Language and Literature. In the Middle Ages a considerable number of Arabic words were added to the language, because of the prestige among French scholars of Arabic science and because the French brought the words back from Arabic lands that they had invaded during the Crusades. Among the words of Arabic derivation in French are chiffre ("number"), épinard ("spinach"), and jupe ("skirt").

The 14th and 15th centuries, the period of the Hundred Years' War between France and England, which devastated French territory, gave popular impetus to French nationalism and to acceptance of the court dialect as a national linguistic standard. The 16th century brought a great advance in linguistic development. In the early 17th century the poet François de Malherbe, through his poetic and critical works, succeeded in establishing a standard of exactness in the use of French words. That standard shaped the language into a sophisticated instrument for the clear, concise expression of thought. One of the most important steps toward standardizing and otherwise improving the French language was the compilation, in the 17th century, of a dictionary by the French Academy, a literary society formed in 1635 by the statesman and cardinal Richelieu. The Academy began the compilation of an official French dictionary in 1639; the first edition appeared in 1694 and was followed by seven others; the eighth appeared in 1932-35. During the reign of Louis XIV, the French language reached the highest point of importance in its history, becoming an international language in Europe, especially for diplomats and scientists.

By the 17th century the French language had developed into what is essentially its present form. Inflectional endings inherited from Latin had been for the most part dropped, and the language depended instead on prepositional phrases and word order to indicate syntactical relationships between words. Publication of the dictionary, widespread literacy, and the extensive use of printing all contributed to the stabilization of the language. Changes occurring later in French were virtually limited to the slow modification of pronunciation and to the addition of new words. The wars with Italy in the first half of the 16th century had resulted in the introduction of about 800 words, for the most part of two types: those derived from the arts, such as fugue and opéra; and military terms, such as colonel and soldat. French wars with Spain in the early part of the 17th century enriched the French language with about 200 words, including cigare and nègre. French wars with Germany in the 17th century resulted in the introduction of a small number of words from German, such as blocus ("blockage" ) and cible ("target"). A section of the newly founded (1795) Institut de France, successor of the old French Academy, issued an edition of the dictionary in 1798; the appendix of the work included a number of words that had been coined since the outbreak of the French Revolution. Among those that survive in the French language are divorcer ("to divorce"), guillotiner ("to behead with a guillotine"), and bureaucrate ("bureaucrat").

In the 16th and 17th centuries French replaced Latin as a common language for international, especially diplomatic, communication in Europe, and it continues to be used for that purpose. It is one of the working languages of the Secretariat of the United Nations.