The terms California Impressionism and California Plein-Air Painting describe the large movement of 20th century artists who worked out of doors (en plein air), directly from nature in California, United States. Their work became popular in the San Francisco Bay Area and Southern California in the first three decades after the turn of the 20th century. Considered to be a regional variation on American Impressionism, the California Impressionists are a subset of the California Plein-Air School.