Verlan (pronounced [vɛʁlɑ̃] ^ⓘ) is a type of argot in the French language, featuring inversion of syllables in a word, and is common in slang and youth language. It rests on a long French tradition of transposing syllables of individual words to create slang words. The word verlan itself is an example of verlan (making it an autological word). It is derived from inverting the sounds of the syllables in l'envers ([lɑ̃vɛʁ], "the inverse", frequently used in the sense of "back-to-front"). The first documented use of verlan dates back to the 19th century, among robbers.

Words in verlan are formed by switching the order in which syllables from the original word are pronounced. For example, français [fʁɑ̃sɛ] becomes céfran [sefʁɑ̃].

Verlan generally retains the pronunciation of the original syllables. However, French words that end in a ⟨e⟩ muet (such as femme [fam]) and words that end in a pronounced consonant (such as flic [flik]) gain the sound [œ] once reversed. In addition, verlan often drops the final vowel sound after the word is inverted, so femme and flic become meuf ([mœf] – meufa in full form) and keuf ([kœf] – keufli in full form), respectively.

The study of written verlan is difficult as it is primarily passed down orally, without standardized spelling. While some still argue that the letters should be held over from the original word, in the case of verlan, most experts agree that words should be spelled as to best approximate pronunciation. For example, verlan is preferred to versl'en. The French author Auguste Le Breton uses numerous examples of verlan, for instance in Du rififi chez les hommes.

Different rules apply for one-syllable words, and words with more than two syllables may be verlan-ised in more than one way. For example, cigarette may yield garetsi or retsiga.

Some verlan words, such as meuf, have become so commonplace that they have been included in the Petit Larousse. The purpose of verlan is to create a somewhat secret language that only its speakers can understand. Words becoming mainstream is counterproductive. As a result, such newly common words may be reversed a second time .

Some verlan words, which are now well incorporated in common French language, have taken on their own significance, or at least certain connotations that have changed their meaning. For example, the word meuf, which can still be used to refer to any woman, also refers to the speaker's girlfriend when used in the possessive form (ma meuf → my girl); while the original word femme would refer to the speaker's wife when used in the same way (ma femme → my wife). Such words retain a cultural significance from the time at which they appeared in common language. Widespread in the second half of the 20th century, beur and beurette (from arabe) refer to people of northern African descent who live in France. The word rebeu (a double verlan) is much more recent, and evolved to refer more generally to people of Arab descent who live in France.

In theory, any word can be made into a verlan, but only a few expressions are used in everyday speech. Verbs translated into verlan cannot be conjugated easily. There is no such thing as a verlan grammar, so generally verbs are used in the infinitive, past participle or progressive form. For example: