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Here is a pretty detailed description of both.

Art Nouveau style is characterized by flowing lines and natural subjects and came into style in the late 19th century. Art deco came along after WW1 in the 1920’s. Art deco design is geometric and often uses bold outlines. It is very spare and streamlined in most cases. it was popular through the 1930’s. HTH Nancy

Arachne gave you a pretty darn good summation. Art Nouveau was also a reaction to the urbanization that occurred during the industrial revolution. This is where all of the natural subjects such as dragonfly shaped broaches and the like come into play. Art Deco, by contrast introduced two elements that carry through to today’s contemporary style. The first is the sleeker look (which becomes even more minimalist in the contemporary style). The second is that during art deco, the artists started playing and experimenting with more industrial materials such as thicker glass, different metals, etc. One way to think of it is that art nouveau was an urban setting reaching back to nature that they weren’t seeing in the city. Art deco embraced modernity and industry.

Here’s a good link that compares the [URL removed] [URL removed]

Art Deco was a popular design movement from 1920 until 1939, affecting the decorative arts such as architecture, interior design, and industrial design, as well as the visual arts such as fashion, painting, the graphic arts, and film. This movement was, in a sense, an amalgam of many different styles and movements of the early 20th century, including Constructivism, Cubism, Modernism, Bauhaus, Art Nouveau, and Futurism