http://www.artic.edu/artaccess/AA_Impressionist/

In the late 19th century, the Impressionists defied academic tradition in French art with their emphasis on modern subjects, sketchlike technique, and practice of painting in the open air with pure, high-keyed color. In the wake of the Impressionist revolution, a new generation of Post-Impressionists pushed the basic pictorial components of color, line, and composition into new psychological and formal territories, influencing many abstract artists of the early 20th century. Thanks to such pioneering donors as Mrs. Potter Palmer and Frederic Clay Bartlett, The Art Institute of Chicago houses one of the largest and most significant collections of Impressionist and Post-Impressionist art in the world.