a Romance language spoken in Spain (the provinces of Lérida, Gerona, Barcelona, Tarragona, Castellón, Valencia, Alicante, and the Balearic Islands), France (the Pyrénées-Orientales), Andorra and parts of Cuba and Argentina.

in Italy Catalan is spoken in the city of Alghero in the North-West of  Sardinia by some 20.000 people.

according to the 1996 census, 95% of the population of Catalonia understand Catalan, and about 79% can speak it. In relation to the Balearic Islands and Valencia, the source  of data available is the 1986 census which indicates that 90% of the population on the Balearic Islands understands Catalan and 72% speak it, and that 74% of the population of Valencia understand Catalan and nearly 50% also speak it. (eurolang.net)

there are two main dialect groups in modern Catalan: Occidental, subdivided into West Catalan and Valencian; and Oriental, subdivided into East Catalan, Balearic, and Roussillonnais and including the dialect spoken in Alghero, Sardinia, where Catalan was introduced in the 14th century. These various dialects are easily mutually intelligible.

Catalan is most closely related to the Occitan language of southern France and to Spanish.