L'art urbain, ou «street art», est un mouvement artistique contemporain. Il regroupe toutes les formes d’art réalisées dans la rue, ou dans des endroits publics, et englobe diverses techniques telles que le graffiti, la réclame, le pochoir, la mosaïque, les stickers, l'affichage voire le yarn bombing ou les installations. C'est principalement un art éphémère vu par un très grand public.

Histoire
La généalogie de l'art urbain est multiple et complexe. Il existe depuis les années 1960 une prise en compte de l'environnement urbain dans la création contemporaine. Allan Kaprow, un des premiers artistes à utiliser les installations, écrit que  :

«l'art s'est déplacé de l'objet spécialisé en galerie vers l'environnement urbain réel.»

En France, les années 1960 voient également des expérimentations d'intégration de l'art dans la ville. L'une des premières expériences est l'organisation d'un symposium international de sculpture, en 1968 à Grenoble, qui impulse la création de dizaines d'œuvres dans la ville, dont celles de Mizui, Vasarely, Calder… En 1972, à Villeneuve de Grenoble, des plasticiens sont contactés pour participer à la conception du volume de la galerie de l'Arlequin. Des contacts sont pris avec Jean Dewasne mais la tentative tourne court. La décoration est finalement confiée à Henri Ciriani et Borja Huidobro. Une fresque est réalisée sur la nouvelle bourse du travail par Ernest Pignon-Ernest, considéré comme l'un des précurseurs de l'art urbain. D'autres expériences sont imaginées dans les villes nouvelles, comme à Évry, en 1972, et à Marne-la-Vallée.
L'art urbain puise ses origines dans des disciplines graphiques aussi variées que la bande dessinée ou l'affiche. Selon Alain Weill, spécialiste mondial de l'affiche (à ne pas confondre avec l'homme d'affaires du secteur des médias…), l'essence de l'art urbain contemporain se retrouve tant dans les œuvres des affichistes d'après-guerre comme Raymond Savignac, en France, que dans celles des dessinateurs de la contre-culture américaine tels Robert Crumb ou Vaughn Bodé, tous deux figures de proue du comics underground depuis les années 1960.
L'art urbain commence à s'épanouir en France à partir de Mai 1968.

Styles
Les artistes d'art urbain ont en commun une activité (légale ou non) d'interventions urbaines. La principale distinction avec le graffiti «traditionnel» (ou hip-hop, tel qu'il est né aux États-Unis), est que les artistes urbains n'ont pas systématiquement recours à la lettre (comme c'est le cas dans le writing américain) et à l'outil aérosol.
Les buts sont variés : dans le cas du graffeur, il s'agit principalement d'apposer son nom ou «blaze» ; dans le cas du street art il s'agit d'une image, "d'une signature visuelle" quelle que soit la méthode. On peut citer les affiches peintes de Jean Faucheur, les sérigraphies de Ernest Pignon-Ernest, les pochoirs de Miss.Tic ou de Jef Aérosol, les autocollants de Clet Abraham, les collages de Kim Prisu petites peintures uniques sur divers support, les peintures au pinceau de Jérôme Mesnager ou celles à l'aérosol de M. Chat ou bien encore les photographies d'Antonio Gallego. D'autres sont motivés par l'expression de messages. Leurs intentions sont politiques comme les membres du groupe VLP (Vive La Peinture) qui collent leur fameux Zuman Kojito dans les rues de Paris surmonté de bulles lui faisant dire des phrases fondamentales du type : «J'existe», «Je résiste», «Je suis un morceau d'utopie», etc. Leur identité visuelle reste cependant bien reconnaissable.
La plupart des artistes souhaitent avant tout s'exprimer et que leurs œuvres soient vues par la foule des usagers de l'espace public qui finit par mémoriser ses "signature visuelle", leur permettant d'accéder à une forme de célébrité individuelle à laquelle ils aspirent le plus souvent. Il existe des exceptions. Yann Dumoget par exemple, inverse la pratique du tag. Au lieu de réaliser des graffitis dans l’espace public, il demande au public de «graffiter» l’espace intime de ses propres peintures. D'autres, comme Cedric Bernadotte questionnent l'espace public en proposant de se réapproprier un lieu avec des matériaux économiques et accessibles tels que le cellophane. Dans les mouvements récents on trouve le mélange du graffiti et de la vidéo ; ainsi le travail d'un artiste comme Blu qui fait de l'animation depuis la rue.

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Street art is visual art created in public locations, usually unsanctioned artwork executed outside of the context of traditional art venues. The term gained popularity during the graffiti art boom of the early 1980s and continues to be applied to subsequent incarnations. Stencil graffiti, wheatpasted poster art or sticker art, and street installation or sculpture are common forms of modern street art. Video projection, yarn bombing and Lock On sculpture became popularized at the turn of the 21st century.
The terms "urban art", "guerrilla art", "post-graffiti" and "neo-graffiti" are also sometimes used when referring to artwork created in these contexts. Traditional spray-painted graffiti artwork itself is often included in this category, excluding territorial graffiti or pure vandalism.
Artists who choose the streets as their gallery are often doing so from a preference to communicate directly with the public at large, free from perceived confines of the formal art world. Street artists sometimes present socially relevant content infused with esthetic value, to attract attention to a cause or as a form of "art provocation".
Street artists often travel between countries to spread their designs. Some artists have gained cult-followings, media and art world attention, and have gone on to work commercially in the styles which made their work known on the streets.

Background
Artists have challenged art by situating it in non-art contexts. Street artists do not aspire to change the definition of an artwork, but rather to question the existing environment with its own language. The motivations and objectives that drive street artists are as varied as the artists themselves. ‘Street’ artists attempt to have their work communicate with everyday people about socially relevant themes in ways that are informed by esthetic values without being imprisoned by them. There is a strong current of activism and subversion in urban art. Street art can be a powerful platform for reaching the public and a potent form of political expression for the oppressed, or people with little resources to create change. Common variants include adbusting, subvertising and other culture jamming, the abolishment of private property and reclaiming the streets.
Some street artists use "smart vandalism" as a way to raise awareness of social and political issues. Other street artists simply see urban space as an untapped format for personal artwork, while others may appreciate the challenges and risks that are associated with installing illicit artwork in public places. A universal motive of most, if not all street art, is that adapting visual artwork into a format which utilizes public space allows artists who may otherwise feel disenfranchised to reach a much broader audience than traditional artwork and galleries normally allow.
Whereas traditional graffiti artists have primarily used free-hand aerosol paints to produce their works, "street art" encompasses many other media and techniques, including: LED art, mosaic tiling, murals, stencil art, sticker art, "Lock On" street sculptures, street installations, wheatpasting, woodblocking, and yarn bombing. New media forms such as projection onto large city buildings are an increasingly popular tool for street artists—and the availability of cheap hardware and software allows street artists to become more competitive with corporate advertisements. Much like open source software, artists are able to create art for the public realm from their personal computers, similarly creating things for free which compete with companies making things for profit.
Street art is a topical issue. Some people consider it a crime, others consider it a form of art. Street artists may be charged with vandalism, malicious mischief, intentional destruction of property, criminal trespass, or antisocial behavior. Legal definitions vary between jurisdictions. In some cities, it is unlawful for landowners to allow any graffiti on their property if it’s visible from any other public or private property.

Origins
Slogans of protest and political or social commentary graffitied onto public walls are the precursor to modern graffiti and street art, and continue as one aspect of the genre. Street art in the form of text or simple iconic graphics in the vein of corporate icons become well-known yet enigmatic symbols of an area or an era.
Some credit the Kilroy Was Here graffiti of the World War II era as one such early example; a simple line-drawing of a long-nosed man peering from behind a ledge. Author Charles Panati indirectly touched upon the general appeal of street art in his description of the "Kilroy" graffiti as "outrageous not for what it said, but where it turned up".
Much of what can now be defined as modern street art has well-documented origins dating from New York City's graffiti boom, with its infancy in the 1960s, maturation in the 1970s, and peaking with the spraypainted full-car subway train murals of the 1980s centered in the Bronx.
As the 1980s progressed, a shift occurred from text-based works of early in the decade to visually conceptual street art such as Richard Hambleton's shadow figures (pictured above). These years coincide with Keith Haring's subway advertisement subversions and Jean-Michel Basquiat's SAMO tags. What is now recognized as "street art" had yet to become a realistic career consideration, and offshoots such as stencil graffiti were in their infancy. Wheatpasted poster art used to promote bands and the clubs where they performed evolved into actual artwork or copy-art and became a common sight during the 1980s in cities worldwide. The group working collectively as AVANT were also active in New York during this period. Punk rock music's subversive ideologies were also instrumental to street art's evolution as an art form during the 1980s.

Early iconic works
The northwest wall of the intersection at Houston Street and the Bowery in New York City has been a target of artists since the 1970s.
The site, now sometimes referred to as the Bowery Mural, originated as a derelict wall which graffiti artists used freely. Keith Haring once commandeered the wall for his own use in 1982. After Haring, a stream of well-known street artists followed, until the wall had gradually taken on prestigious status. By 2008, the wall became privately managed and made available to artists by commission or invitation only.
A series of I AM THE BEST ARTIST René murals painted by René Moncada began appearing on the streets of SoHo in the late 1970s. René has described the murals as a thumb in the nose to the art community he felt he'd helped pioneer but by which he later felt ignored. Recognized as an early act of "art provocation", they were a topic of conversation and debate at the time, and related legal conflicts raised discussion about intellectual property, artist's rights, and the First Amendment. The ubiquitous murals (pictured above) also became a popular backdrop to photographs taken by tourists and art students, and for advertising layouts and Hollywood films. IATBA murals were often defaced, only to be repainted by René.

Exhibitions
In 1981, Washington Project for the Arts held an exhibition entitled Street Works, which included urban art pioneers such as John Fekner, Fab Five Freddy and Lee Quinones working directly on the streets.
Fekner, who once defined street art as "all art on the street that’s not graffiti", is included in Cedar Lewisohn’s book Street Art: The Graffiti Revolution, which accompanied the 2008 Street Art exhibition at the Tate Modern in England, of which Lewisohn was the curator.