The musical Art Nouveau was developed in Catalonia, as the architectonic and the artistic one, essentially, between the years 1890 and 1920. Its origins are also common and are located in England between the years 1850-1880 (see Art Nouveau).
The same as in other arts, the Art Nouveau is defined in music by freedom in artistic composition in search of authenticity more than beauty. This tendency is clearly manifested in the interest of Modernist (Art Nouveau) musicians in the folkloric and popular music - this is specially the case of Albéniz, Granados, Nicolau and Morera -. In Catalonia, in addition, a strong national feeling is also present in the compositions: Millet with "El cant de la Senyera" - the "Senyera song" (a song in homage of Catalan flag) -, as an example. 
Other specific element of Catalan Art Nouveau music is the "Wagnerisme" - the influence of Wagner - which is very clear in the works of some Catalan composers during the first quarter of the XXth century, Barcelona being one of the most "wagnerian" cities in the world.
The musical Art Nouveau hasn't a proper school and the musicians are classified more by the period in which they developed his activity, that because they where self classified into the movement. Morera is perhaps an exception because he was more strongly involved in all the activities of Modernists. In that way it is interesting to remember his active participation in the "Festes Modernistes" - Art Nouveau festivals - organized by Santiago Rusiñol in Sitges. The presence of musicians in the Modernist (Art Nouveau) meetings of "Quatre Gats" was also very intensive. 
This lack of a Modernist musical school, is the reason that the criteria to include or not some musicians into the movement are diverse. In this way some authors consider also Art Nouveau musicians Josep Anselm Clavé - died in 1874, before the start of the movement - perhaps due to his dedication to popular music - could be classified as pre-modernist -.