PLEIN AIR GROUPS
  International Plein Air Painters
  Laguna Plein Air Painters Association
  PleinAirArt.net - a listing of all plein air events across the nation
  Plein Air Florida
  Plein Air Painters of America
  Southern California Plein Air Painters Association
  Tucson Plein Air Painters' Society

LOCAL TO DC
  Maryland Pastel Society
  Maryland State Arts Council

MID-ATLANTIC
  Cape May County Art League
  Mid-Atlantic Plein Air Painters Association
  Plein Air Painters of the Jersey Coast

NATIONAL
  American Impressionist Society
  International Association of Pastel Societies
  Oil Painters of America
  Pastel Society of America
  World Federation of Miniaturists

INTERNATIONAL
  Landscape Artists International