Plein Air is the French for open air. The term is used to describe the practice of artists painting before a landscape or other chosen subject out of doors, rather than in a studio or workshop. Before the end of the 18th century outdoor work was usually restricted to drawings and watercolours, but in the 19th century the increasing popularity of sketching landscapes in oil developed gradually into the practice of painting finished pictures in front of the motif.
Artists such as Corot and Daubigny frequently painted out of doors, but it was the Impressionists who embraced plein-air painting with the greatest enthusiasm.