Assemblage is an artistic form or medium usually created on a defined substrate that consists of three-dimensional elements projecting out of or from the substrate. It is similar to collage, a two-dimensional medium. It is part of the visual arts, and it typically uses found objects, but is not limited to these materials. 
The origin of the art form dates to the cubist constructions of Pablo Picasso c. 1912-1914. The origin of the word (in its artistic sense) can be traced back to the early 1950s, when Jean Dubuffet created a series of collages of butterfly wings, which he titled assemblages d'empreintes. However, both Marcel Duchamp, Pablo Picasso and others had been working with found objects for many years prior to Dubuffet. Russian artist Vladimir Tatlin created his "counter-reliefs" in the mid 1910s. Alongside Tatlin, the earliest woman artist to try her hand at assemblage was Elsa von Freytag-Loringhoven, the Dada Baroness. In Paris in the 1920s Alexander Calder, Jose De Creeft, Picasso and others began making fully 3-dimensional works from metal scraps, found metal objects and wire. In the U.S., one of the earliest and most prolific assemblage artists was Louise Nevelson, who began creating her sculptures from found pieces of wood in the late 1930s.
John Chamberlain (1927-2011), a Chicago artist known for his sculptures of welded pieces of wrecked automobiles.
Greg Colson (born 1956), an American artist known for his wall sculptures of stick maps, constructed paintings, solar systems, directionals, and intersections.
Joseph Cornell (1903–1972). Cornell, who lived in New York City, is known for his delicate boxes, usually glass-fronted, in which he arranged surprising collections of objects, images of renaissance paintings and old photographs. Many of his boxes, such as the famous Medici Slot Machine boxes, are interactive and are meant to be handled.
Raoul Hausmann (1886–1971), an Austrian artist and writer and a key figure in Berlin Dada, his most famous work is the assemblage Der Geist Unserer Zeit - Mechanischer Kopf (Mechanical Head [The Spirit of Our Age]), c. 1920.
Romauald Hazoumé (born 1962), a contemporary artist from the Republic of Bénin, who exhibits widely in Europe and the U.K.
George Herms (born 1935), an American artist known for his assemblages, works on papers, and theater pieces.
Jasper Johns (born 1930), an American Pop artist, painter, printmaker and sculptor.
Edward Kienholz (1927–1994), an American artist who collaborated with his wife, Nancy Reddin Kienholz, creating free-standing, large-scale "tableaux" or scenes of modern life such as the Beanery, complete with models of persons, made of discarded objects.
Janice Lowry (1946-2009), American artist known for biographical art in the form of assemblage, artist books, and journals, which combined found objects and materials with writings and sketches.
Ondrej Mares (1949–2008), a Czech-Australian artist and sculptor best known for his 'Kachina' figures - a series of works.
Markus Meurer (born 1959), a German artist, known for his sculptures from found objects
Louise Nevelson (1899–1988), an American artist, known for her abstract expressionist “boxes” grouped together to form a new creation. She used found objects or everyday discarded things in her “assemblages” or assemblies, one of which was three stories high.
Betye Saar (born 1926), American visual artist primarily known for her assemblages with family memorabilia, stereotyped African American figures from folk culture and advertising, mystical amulets and charms, and ritual and tribal objects.
Daniel Spoerri (born 1930), a Swiss artist, known for his "snare pictures" in which he captures a group of objects, such as the remains of meals eaten by individuals, including the plates, silverware and glasses, all of which are fixed to the table or board, which is then displayed on a wall.
Vladimir Tatlin (1885–1953), a Russian artist known for his counter-reliefs — structures made of wood and iron for hanging in wall corners in the 1910s.
Wolf Vostell (1932–1998), known for his use of concrete in his work. In his environments video installations and paintings he used television sets and concrete as well as telephones real cars and pieces of cars.
William C. Seitz: The Art of Assemblage. Exhib. October 4 - November 12, 1961, The Museum of Modern Art, New York, 1961.
Stephan Geiger: The Art of Assemblage. The Museum of Modern Art, 1961. Die neue Realität der Kunst in den frühen sechziger Jahren, (Dissertation Universität Bonn 2005), München 2008, ISBN 978-3-88960-098-1
Sophie Dannenmüller: "Un point de vue géographique: l'assemblage en Californie", in L'art de l'assemblage. Relectures, sous la direction de Stéphanie Jamet-Chavigny et Françoise Levaillant. Presses universitaires de Rennes, collection "Art & société", Rennes, 2011.
Sophie Dannenmüller: "L'assemblage en Californie: une esthétique de subversion", in La Fonction critique de l'art, Dynamiques et ambiguïtés, sous la direction de Evelyne Toussaint, Les éditions de La Lettre volée / Essais, Bruxelles, 2009.
Sophie Dannenmüller: "Bruce Conner et les Rats de l'Art", Les Cahiers du Musée national d'art moderne, Editions du Centre Pompidou, Paris, n° 107, avril 2009, p. 52-75.