French orthography encompasses the spelling and punctuation of the French language. It is based on a combination of phonemic and historical principles. The spelling of words is largely based on the pronunciation of Old French c. 1100–1200 AD, and has stayed more or less the same since then, despite enormous changes to the pronunciation of the language in the intervening years. Even in the late 17th century, with the publication of the first French dictionary by the Académie française, there were attempts to reform French orthography.

This has resulted in a complicated relationship between spelling and sound, especially for vowels; a multitude of silent letters; and many homophones, e.g. saint/sein/sain/seing/ceins/ceint (all pronounced [sɛ̃]) and sang/sans/cent (all pronounced [sɑ̃]). This is conspicuous in verbs: parles (you speak), parle (I speak / one speaks) and parlent (they speak) all sound like [paʁl]. Later attempts to respell some words in accordance with their Latin etymologies further increased the number of silent letters (e.g., temps vs. older tans – compare English "tense", which reflects the original spelling – and vingt vs. older vint).

Nevertheless, the rules governing French orthography allow for a reasonable degree of accuracy when pronouncing unfamiliar French words from their written forms. The reverse operation, producing written forms from pronunciation, is much more ambiguous. The French alphabet uses a number of diacritics, including the circumflex, diaeresis, acute, and grave accents, as well as ligatures. A system of braille has been developed for people who are visually impaired.

The French alphabet is based on the 26 letters of the Latin alphabet, uppercase and lowercase, with five diacritics and two orthographic ligatures.

⟨w⟩ and ⟨k⟩ are rarely used except in loanwords and regional words. /w/ is usually written ⟨ou⟩; /k/ is usually written ⟨c⟩ anywhere but before ⟨e, i, y⟩, ⟨qu⟩ before ⟨e, i, y⟩, and sometimes ⟨que⟩ at the ends of words. However, ⟨k⟩ is common in the metric prefix kilo- (originally from Greek χίλια khilia "a thousand"), e.g. kilogramme, kilomètre, kilowatt, kilohertz.

The diacritics used in French orthography are the acute accent (⟨◌́⟩; accent aigu), the grave accent (⟨◌̀⟩; accent grave), the circumflex (⟨◌̂⟩; accent circonflexe), the diaeresis (⟨◌̈⟩; tréma), and the cedilla (⟨◌̧⟩; cédille). Diacritics have no effect on the primary alphabetical order.

A tilde (⟨◌̃⟩) above ⟨n⟩ is occasionally used in French for words and names of Spanish origin that have been incorporated into the language (e.g., El Niño, piñata). Like the other diacritics, the tilde has no impact on the primary alphabetical order.

Diacritics are often omitted on capital letters, mainly for technical reasons (not present on AZERTY keyboards). However, many authorities, including the Académie française and the Office québécois de la langue française, reject this usage. The Académie states that, because accents in French have full orthographic value and their absence can lead to misreading and mispronunciation, good typography must systematically use diacritics on capital letters. There is an exception for acronyms but not for abbreviations (e.g., CEE, ALENA, but É.-U.). Nevertheless, diacritics are often ignored in word games, including crosswords, Scrabble, and Des chiffres et des lettres.