The term "plein-air" literally translates into "open air." The term is largely associated with the Impressionist artists of the late 1800s, a time when artists began to paint subject matter not normally seen: real people doing real, everyday things. And they came out of their studios into the open air to do so. "Nature knows no black or white--nature knows no line." This quote was well known among the early Impressionist artists, including Claude Monet. When Monet painted his Rouen Cathedral Series, he observed the Cathedral from his flat across the street during different times of the day. From this observation, he noticed the Cathedral would actually change color, depending on the location and intensity of the sun that day. The result of Monet's work were colorful and energetic paintings that captured the spontaneity of nature's light. The Encyclopedia Britannica elaborates this point: "The Impressionists were very much interested in the effects that light had on different objects during certain times of the day. Whether the object was a tree, an apple or a human being really didn't matter much. There was no time for contemplating subject matter when artists were busy realizing that what is green in the morning, might be yellow, or even red, in the afternoon--depending on the intensity and location of the sun. Artists also became aware that everything had color--even a shadow, known before as only gray--could contain wonderful hues of violet or blue." En plein air artists attempt to capture an immediate impression of what the eye sees at a single glance, rather than what the viewer knows or feels about the work. They study how light appears on subjects in different weather and at different times of the day, an interest that can be traced back to Realism. They prefer to work outdoors in natural light, rather than in their studio with sketches, and their art tends to have brilliant colors that almost shimmer in their intensity. Critics of Impressionism complained that the artists did not follow the traditional rules of composition. Indeed, the Impressionists' subjects often appeared informal and spontaneous. Their paintings were an expression of the life they saw around them: rural scenes, city life, and people dressed in everyday clothing going about their business. Criticism was also directed at the sketchiness of Impressionistic style, with its quick, visible brushstrokes. Critics said the pictures did not look finished, and that the work was sloppy. An acronym was coined to define the five issues important to most Impressionists who paint en plein air: E Everyday life L Light B Brushstrokes OOutdoor setting W Weather and atmosphere In essence, Impressionists artists attempt to paint candid glimpses of their subjects showing the effects of sunlight on things at different times of day. The Plein-Air Painters of American provide an in-depth explanation about plein-air painting on their website: http://www.p-a-p-a.com/whatis.html