Leonese (llionés, ḷḷionés, lionés) is a set of vernacular Romance language varieties spoken in northern and western portions of the historical region of León in Spain (the modern provinces of León, Zamora, and Salamanca), the village of Riudenore (in both Spain and Portugal) and Guadramil in Portugal, sometimes considered another language. In the past, it was spoken in a wider area, including most of the historical region of Leon. The current number of Leonese speakers is estimated at 20,000 to 50,000. Spanish is now the predominant language in the area.

Leonese forms part of the Asturleonese linguistic group along with dialects of Asturian. The division between Asturian and Leonese is extra-linguistic, as the main divisions within the Asturleonese complex are between eastern and western varieties, rather than between varieties spoken in Asturias and Leon.

Menéndez Pidal used "Leonese" for the entire linguistic area, including Asturias. This designation has been replaced by Ibero-Romance scholars with "Asturian-Leonese", but "Leonese" is still often used to denote Asturian-Leonese by non-speakers of Asturian or Mirandese. Sometimes the language as a whole is simply called "Asturian" for several reasons, such as the Leonese dialects being on the brink of extinction, or the widespread ignorance of its very existence (even in León), as well as their lack of recognition and institutional support (as opposed to their Asturias counterparts).

In a narrow geographical sense, Leonese is distinct from the dialects grouped under the Asturian language. However, the division between Leonese and Asturian is due to the distinctly different identities of both areas, separated by a mighty mountain range, while the dialects have enough common traits to consider them part of a single language, Astur-Leonese or Asturian-Leonese. The principal isoglosses in this region do not divide Asturias and Leon, dialectal areas (western, central, eastern) are in fact shaped along a north-south axis (thus encompassing lands both north and south of the mountains, both in Asturias and in Castile and León). In the west of Asturias and Leon, dialects of Asturo-Leonese begin to transition into the closely related Galician language, with the westernmost variants effectively constituting dialects of Galician.

On the other hand, Menéndez Pidal and fellow scholars discussed a "Leonese language" descending from Latin and encompassing two groups: the Asturian dialects on one hand, and dialects spoken in the provinces of León and Zamora in Spain and a related dialect in Trás-os-Montes (Portugal), on the other hand.

The Asturleonese dialect (considered part of the Leonese dialects) of Miranda do Douro (Portugal), Mirandese, is most certainly a dialect on its own, considering the numerous differences it has when compared to dialects in the Spanish side. In fact, it is often considered as a separate language, especially in Portugal, where it has been granted official recognition, and is regulated by the Institute of the Mirandese Language. Thus, Asturleonese is sometimes considered a group of two languages, Asturian or Asturleonese proper, and Mirandese.

Unlike Asturian, which is regulated by the Academy of the Asturian Language (ALLA) and promoted by the Asturian Government and local legislation, the Leonese dialects are not officially promoted or regulated.

In Leonese, any of five vowel phonemes, /a, e, i, o, u/, may occur in stressed position. In the unstressed positions, the distinction between close and mid vowels is neutralized in favor of the archiphonemes /ɪ/ and /ʊ/.