Occitan (English pronunciation: /ˈɒksɪˌtæn/,Occitan: [uksiˈta] or [utsiˈta]), known also as Lenga d'òc (Occitan: [ˈleŋɡɔ ˈðɔ(k)]; French: Langue d'oc), is a Romance language spoken in southern France, Italy's Occitan Valleys, Monaco, and Spain's Val d'Aran: the regions sometimes known unofficially as Occitania. It is also spoken in the linguistic enclave of Guardia Piemontese (Calabria, Italy).

It is an official language in Catalonia, Spain (known as Aranese in Val d'Aran). Occitan's closest relative is Catalan. Since September 2010, the Parliament of Catalonia has considered Aranese Occitan to be the officially preferred language for use in the Val d'Aran.

The term Provençal (Occitan: provençal, provençau or prouvençau, IPA: [pruβenˈsal, pʀuveⁿˈsaw]) may be used as a traditional synonym for Occitan but, nowadays, “Provençal” is mainly understood as an Occitan dialect spoken in Provence.

The long-term survival of Occitan is in grave doubt. According to the UNESCO Red Book of Endangered Languages, four of the six major dialects of Occitan (Provençal, Auvergnat, Limousin and Languedocien) are considered "severely endangered", while the remaining two (Gascon and Vivaro-Alpine) are considered "definitely endangered" ("severely endangered" essentially means that only elderly people still speak the language fluently, while "definitely endangered" means that adults speak the language but are not passing it on to their children).