Art Nouveau - French for "The New Art." An international art movement and style of decoration and architecture of the late nineteenth and early twentieth centuries, characterized particularly by the curvilinear depiction of leaves and flowers, often in the form of vines. These might also be described as foliate forms, with sinuous lines, and non-geometric, "whiplash" curves. Gustav Klimt (Austrian, 1862-1918), Alphonse Mucha (Czechoslovakian, 1860-1939), Henri de Toulouse-Lautrec (French, 1861-1901), Aubrey Beardsley (English, 1872-1898), Antonio Gaudí (Spanish, 1852-1926), and Hector Guimard (French, 1867-1942) were among the most prominent artists associated with this style. The roots of Art Nouveau go back to Romanticism, Symbolism, the English Arts and Crafts Movement and William Morris (English, 1834-1896). In America, it inspired, among others, Louis Comfort Tiffany (1848-1933). The name is derived from "La Maison de l'Art Nouveau," a gallery for interior design that opened in Paris in 1896. Art Nouveau is known in Germany as Jugenstil and in England as Yellow Book Style, and epitomizes what is sometimes called fin de siècle style. It reached the peak of its popularity around 1900, only to be gradually overtaken by art deco and other modernist styles.

(Read more at the source: Artlex.com)

Decorative style of the late 19th century and the early 20th that flourished principally in Europe and the USA. Although it influenced painting and sculpture, its chief manifestations were in architecture and the decorative and graphic arts, the aspects on which this survey concentrates. It is characterized by sinuous, asymmetrical lines based on organic forms; in a broader sense it encompasses the geometrical and more abstract patterns and rhythms that were evolved as part of the general reaction to 19th-century historicism. There are wide variations in the style according to where it appeared and the materials that were employed.

Michèle Lavallée
From Grove Art Online

Source: moma.org

From the 1880s until the First World War, western Europe and the United States witnessed the development of Art Nouveau ("New Art"). Taking inspiration from the unruly aspects of the natural world, Art Nouveau influenced art and architecture especially in the applied arts, graphic work, and illustration. Sinuous lines and "whiplash" curves were derived, in part, from botanical studies and illustrations of deep-sea organisms such as those by German biologist Ernst Heinrich Haeckel (1834–1919) in Kunstformen der Natur (Art Forms in Nature, 1899). Other publications, including Floriated Ornament (1849) by Gothic Revivalist Augustus Welby Northmore Pugin (1812–1852) and The Grammar of Ornament (1856) by British architect and theorist Owen Jones (1809–1874), advocated nature as the primary source of inspiration for a generation of artists seeking to break away from past styles. The unfolding of Art Nouveau's flowing line may be understood as a metaphor for the freedom and release sought by its practitioners and admirers from the weight of artistic tradition and critical expectations.

Source: metmuseum.org

Although Gaudí was influenced by John Ruskin's analysis of the Gothic early in his career, he sought an authentic Catalan style at a time, the late 19th century, when this region was experiencing a resurgence of cultural and political pride. Ruskin, an English critic, rejected ancient classical forms in favor of the Gothic's expressive, even grotesesque qualities. This interest in the value of medieval architecture resulted in Gaudi being put in charge of the design of Sagrada Família (Sacred Family) shortly after construction had begun.

Gaudí was a deeply religious Catholic whose ecstatic and brilliantly complex fantasies of organic geometry are given concrete form throughout the church. Historians have identified numerous influences especially within the northeast façade, the only part of the church he directly supervised (the remainder of the church, including three of the southwest trancept's four spires are based on his design but were completed after Gaudí's death in 1926), these include African mud architecture, Gothic, Expressionist, of course a varient of Art Nouveau that emphasizes marine forms. 

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