The poster as we know it dates back no further than 1870, for it was then that the perfection of techniques in color lithography first made mass production possible. Yet in little more than a hundred years it has come to be recognized as a vital art form, attracting artists at every level, from painters like Toulouse-Lautrec and Mucha to theatrical and commercial designers, and ranging in style from Art Nouveau, Symbolism, Cubism and Art Deco, to the formality of the Bauhaus and the deliberate incoherence of the hippies and other underground movements in the 1960s. 273 illus., 72 in color.