Art Nouveau was an international style and movement in art, architecture and design that was very popular at the turn of the 20th century, lasting roughtly from 1890-1910. It's name comes from the French for "new art".
Highly influenced by the English Arts and Crafts movement, Art Nouveau was similar to Romanticism, as it was a reaction to industrialization and mass-production. It looked to represent beautiful forms based closely on nature. In Germany, the movement became known as Jugendstil (youth style) after the magazine Jugend.
The Art Nouveau style is very different from Neoclassicism, which preceded it, and is highly decorative and stylized. Art Nouveau made use of new materials, rejecting the neoclassical tradition of hiding modern materials in classical facades. Art Nouveau artists looked to lesser-known and lesser-immitated art movements, like medieval art, Asian art forms, and work that was similarly abstracted and linear, like Celtic and Saxon illuminations and interlaced artwork; Japanese paintings and prints, and ornate motifs of Chinese and Japanese ceramics. Art Nouveau artists were also inspired by scientific discoveries, like microorganism forms, and explorations of botany and zoology.