Although Pop art is now most associated with the work of New York artists of the early 1960s, such as Andy Warhol, Roy Lichtenstein, James Rosenquist and Claes Oldenburg, artists who drew on popular imagery were part of an international phenomenon which saw major developments in various cities from the mid 1950s onwards. Its first appearance was perhaps among members of the Independent Group, who gathered around London, but there would also be important developments simultaneously in New York (in the work of Jasper Johns and Robert Rauschenberg), as well as later in France (among the Nouveau Realistes), in Germany (the 'Capitalist Realism' of Sigmar Polke, Konrad Lueg, and Gerhard Richter), and in Los Angeles (including Ed Ruscha, Billy Al Bengston and others).

• 'Pop' was a term first applied to popular culture rather than to art which borrowed from that culture, but it would be one of the goals of the Pop art movement to blur the boundaries between 'high' art and 'low' popular culture. The notion that there is no hierarchy of culture, and that art may borrow from any source and mix it with others, regardless of their context and history, has been one of the most important characteristics of Postmodernism as a cultural moment.
• Although Pop art encompasses a wide variety of work with very different attitudes and postures, much of it is emotionally cold towards its subject matter. In contrast to the 'hot' expressivism of the gestural abstraction that preceded it, Pop art is generally 'coolly' ambivalent. Whether this suggests an acceptance of the popular world, or a shocked withdrawal, has been the subject of much debate.
• It could be argued that the Abstract Expressionists searched for trauma in the soul, while Pop artists searched for traces of the same trauma in the mediated world of advertising, cartoons and popular imagery at large. But it is perhaps truer to say that Pop artists were the first to recognize that we can have no unmediated access to anything - be it the soul, the natural world, or the built environment. Everything is connected.

In London, in 1952, a group of artists calling themselves the Independent Group began meeting regularly to discuss topics such as mass culture's place in fine art, the found object, and science and technology; members included Edouardo Paolozzi, Richard Hamilton, architects Alison and Peter Smithson, and critics Lawrence Alloway and Reyner Banham. Britain in the early 1950s was still emerging from the austerity of the post-war years, and so its outlook on popular culture coming from America was ambivalent. While the group was suspicious of its commercial character, they were enthusiastic about the rich world pop culture seemed to promise for the future. The imagery they discussed at length included that found in Western movies, science fiction, comic books, billboards, automobile design and rock n' roll music.

The actual term "Pop art" has several possible origins: the first use of the term in print has been attributed to both Lawrence Alloway and Alison and Peter Smithson, while the first artwork to incorporate the word 'Pop' is said to have been produced by Paolozzi. His collage I Was a Rich Man's Plaything (1947) contained cut-up images of a pinup girl, Coca-Cola logo, cherry pie, World War II fighter plane, and a man's hand holding a pistol, out of which burst the world 'POP!' in a puffy white cloud.

The now classic New York Pop art of Warhol and Lichtenstein emerged suddenly in 1960, but it was importantly prefigured some years before in the Neo-Dada work of Jasper Johns and Robert Rauschenberg. By the mid 1950s, Johns was already troubling the conventions of Abstract Expressionism with abstract paintings that included references to, as Johns put it, "things the mind already knows" - targets, flags, hand-prints, letters and numbers. Meanwhile, Rauschenberg's Combines incorporated found objects and screen-printed photographs.

The French equivalent of Pop Art was Nouveau Réalisme, a movement launched by the critic Pierre Restany in 1960. Although it would echo the American's concerns with commercial culture, most of the French artists were more concerned with sculpture than with imagery. Closer to the American model of image-based Pop was the work of German artist Sigmar Polke who, in a manner similar to that of Lichtenstein and Warhol, explored the expressive possibilities of mechanical reproduction.

It is a notable characteristic of the Pop movement that many of its most important figures would have close involvement with commercial art: Ed Ruscha first supported himself as a graphic designer, while James Rosenquist had a spell as a billboard painter. But Andy Warhol was by far the most successful in commercial art and had established a formidable reputation in New York before he ever turned to fine art.

The critic Hal Foster has anatomized Pop art as consisting of essentially five different image types, each of which is preoccupied with a slightly different problem, and each of which has been importantly influential on subsequent artists. The first he locates in the 'tabular' images of Richard Hamilton that were influenced by the collages of Edouardo Paolozzi and others in the Independent Group. Hamilton arranged his motifs on the canvas in a loose fashion and he exploited the lush quality of paint to emphasize the analogies he drew between designed products like cars, and fragments of women's bodies - analogies which were typical of contemporary advertising.

Another type of image typical of Pop, Foster argues, is that epitomized by the screened images of Roy Lichtenstein. Lichtenstein proved that he could fulfill demands for a great picture even though his subject matter derived from popular art: his images delivered the instantaneous punch of good art; they used expressive and abstract forms and the compositions were powerfully unified.

The third image type that Foster identified is best exemplified by the imagery of trauma, death and disaster in the work of Andy Warhol. Some have argued that pictures like White Burning Car, III (1963), with its repeated images of a smoking car wreck, suggest a cold disinterest in the subject matter - as if the repetitions of the mass media had blunted the artists' ability to process emotion. Others have argued the contrary; such images point to Warhol's interest in the horrors of contemporary life. Foster has suggested, instead, that Warhol employed repetition precisely to register trauma - like a horrific image that returns to haunt again and again.

Foster locates a fourth image type in Gerhard Richter's marriage of photography and painting. Instead of leveling the high and the low, Richter's art seems to draw on the vast range of photographs that we encounter every day, to the point of suggesting that nothing can be seen clearly any more without the influence of the photographic image. As in Warhol's work, the suggestion of trauma and death is present in these coldly rendered photographs, but Richter introduces blurs and smears of paint which remind one that these are not photographs we are looking at, but paintings which lie in a grand tradition which has always aspired to memorialize the past. If the photographs represent the threat of forgetting, the sorrow of time lost, the paintings hold out the hope that these memories could be sealed in - painting, in other words, might still have a purpose in the modern world, in preserving memory.

Finally, Foster points to the importance of Ed Ruscha in developing an imagery that responded to the visual landscape of Los Angeles. Ruscha borrowed motifs from commercial art in a similar manner to his colleagues on the East Coast, and often drew analogies between the effects of those motifs and those of high abstract art. Yet Ruscha also learnt much from cinema, and much of his imagery might be said to be reminiscent of the cinematic image, a space that is, as Foster puts it, "at once deep and superficial, illusionist and flat: in the movies space is surface and vice versa and the words (as in credits and subtitles) can appear in the same register as the images."

Although Warhol and Lichtenstein were the first classic Pop artists to emerge in New York in the early 1960s, others quickly followed, including James Rosenquist and Red Grooms. The work of these artists was starkly different from the Neo-Dada artists who had matured in the mid-1950s: instead of working in mixed media, like Johns' targets or Rauschenberg's Combines, the new Pop artists were focused on imagery, particularly that of popular icons such as President Kennedy, Marilyn Monroe, Campbell's soup cans, and scenes from film noir. The central theme in such artworks was the message that certain popular imagery had become so prevalent in our everyday lives that the images themselves were now art, and as such have transcended any division between kitsch and high art.

"Insofar as the flatbed picture plane accommodates recognizable objects, it presents them as man-made things of universally familiar character. The emblematic images of the early Johns belong in this class; so, I think, does most of Pop Art. When Roy Lichtenstein in the early sixties painted an Air Force officer kissing his girl good-bye, the actual subject matter was the mass-produced comic-book image.."
-Leo Steinberg, from "Other Criteria"

"Popular (designed for a mass audience); transient (short-term solution); expendable (easily forgotten); low cost; mass produced; young (aimed at youth); witty; sexy; gimmicky; glamorous; and last but not least, Big Business."
- Richard Hamilton, defining what Pop art means to him