Fils de France (French pronunciation: [fis də fʁɑ̃s], Son of France) was the style and rank held by the sons of the kings and dauphins of France. A daughter was known as a fille de France (French pronunciation: [fij də fʁɑ̃s], Daughter of France).

The children of the dauphin (a title reserved for the king's heir apparent, whether son, grandson or great-grandson of the monarch) were accorded the same style and status as if they were the king's children instead of his grandchildren or great-grandchildren.

The king, queen, queen dowager, enfants de France (children of France) and petits-enfants de France (grandchildren of France) constituted the famille du roi (royal family). More remote legitimate, male-line descendants of France's kings held the designation and rank of princes du sang (princes of the blood) or, if legally recognised despite a bar sinister on the escutcheon, they were customarily deemed princes légitimés (legitimated princes).

The dauphin, the heir to the French throne, was the most senior of the fils de France and was usually addressed as Monsieur le dauphin. The king's next younger brother, also a fils de France, was known simply as Monsieur, and his wife as Madame.

Daughters were referred to by their given name prefaced with the honorific Madame, while sons were referred to by their main peerage title (usually ducal), with the exception of the dauphin. The king's eldest daughter was known as Madame Royale until she married, whereupon the next eldest fille de France succeeded to that style.

Although the children of monarchs are often referred to in English as prince or princess, those terms were used as general descriptions for royalty in France but not as titular prefixes or direct forms of address for individuals (with the exception of Monsieur le Prince for the senior prince du sang) prior to the July Monarchy (1830–1848). Collectively, the legitimate children of the kings and dauphins were known as enfants de France ("children of France"), while examples abound in reputable works of fils de France and fille de France being converted into other languages as "Prince/Princess of France" (however the same works, as cited, leave the Spanish equivalent, Infante/Infanta de España, untranslated). The illegitimate children of French kings, dauphins, and princes du sang were not entitled to any rights or styles per se, but often they were legitimised by their fathers. Even then, however, they were never elevated to the rank of fils de France, although they were sometimes accorded the lower rank and/or privileges associated with the princes du sang.

All enfants de France were entitled to the style of Royal Highness (altesse royale) from the reign of Louis XIII. However, in practice that formal honorific was less often used than the more traditionally French styles of Monsieur, Madame or Mademoiselle. The styles of the royal family varied as follows:

Under the Valois monarchs, the titles borne by the sons of kings became regularized. Philip VI made his eldest son Duke of Normandy and his second son Duke of Orléans. Normandy would have become the regular title of the heirs apparent of kings, but the acquisition of Dauphiné and the request of its last count ensured that the heirs apparent would be called Dauphin instead.