Op art, short for optical art, is a style of visual art that uses distorted or manipulated geometrical patterns, often to create optical illusions. It began in the early 20th century, and was especially popular from the 1960s on, the term "Op art" dating to 1964.

Op artworks are normally abstract, with some better-known pieces created in black and white. Typically, they give the viewer the impression of movement, hidden images, flashing and vibrating patterns, or swelling or warping. In contrast, the much older trompe-l'œil style always represents figurative subjects, which are shown with deceptive three-dimensionality.

Illusionism, focused on the perception of extended space within a flat picture, is found from the earliest points of art history. However, the antecedents of op art, in terms of graphic effects and concern for exotic optical illusions, can be traced back to Neo-Impressionism, Cubism, Futurism, Constructivism, and Dada. The Divisionists, a group of Neo-Impressionist painters, attempted to increase the apparent luminosity of their paintings through recourse to optics and optical illusions. László Moholy-Nagy produced photographic op art and taught the subject in the Bauhaus; one of his lessons consisted of making his students produce holes in cards and then photographing them.

Time magazine coined the term op art in 1964, in response to Julian Stanczak's show Optical Paintings at the Martha Jackson Gallery, to mean a form of abstract art (specifically non-objective art) that uses optical illusions. Works now described as "op art" had been produced for several years before Time's 1964 article. For instance, Victor Vasarely's painting Zebras (1938) is made up entirely of curvilinear black and white stripes not contained by contour lines. Consequently, the stripes appear to both meld into and burst forth from the surrounding background. Also, the early black and white "dazzle" panels that John McHale installed at the This Is Tomorrow exhibit in 1956 and his Pandora series at the Institute of Contemporary Arts in 1962 demonstrate proto-op art tendencies. Martin Gardner featured op art and its relation to mathematics in his July 1965 Mathematical Games column in Scientific American. In Italy, Franco Grignani, who originally trained as an architect, became a leading force of graphic design where op art or kinetic art was central. His Woolmark logo (launched in Britain in 1964) is probably the most famous of all his designs.

Op art perhaps more closely derives from the constructivist practices of the Bauhaus. This German school, founded by Walter Gropius, stressed the relationship of form and function within a framework of analysis and rationality. Students learned to focus on the overall design or entire composition to present unified works. Op art also stems from trompe-l'œil and anamorphosis. Links with psychological research have also been made, particularly with Gestalt theory and psychophysiology. When the Bauhaus was forced to close in 1933, many of its instructors fled to the United States. There, the movement took root in Chicago and eventually at the Black Mountain College in Asheville, North Carolina, where Anni and Josef Albers eventually taught.

Op artists thus managed to exploit various phenomena," writes Frank Popper, "the after-image and consecutive movement; line interference; the effect of dazzle; ambiguous figures and reversible perspective; successive colour contrasts and chromatic vibration; and in three-dimensional works different viewpoints and the superimposition of elements in space.

In 1955, for the exhibition Mouvements at the Denise René gallery in Paris, Victor Vasarely and Pontus Hulten promoted in their "Yellow manifesto" some new kinetic expressions based on optical and luminous phenomenon as well as painting illusionism. The expression kinetic art in this modern form first appeared at the Museum für Gestaltung of Zürich in 1960, and found its major developments in the 1960s. In most European countries, it generally includes the form of optical art that mainly makes use of optical illusions, like op art, as well as art based on movement represented by Yacov Agam, Carlos Cruz-Diez, Jesús Rafael Soto, Gregorio Vardanega or Nicolas Schöffer. From 1961 to 1968, the Groupe de Recherche d'Art Visuel (GRAV) founded by François Morellet, Julio Le Parc, Francisco Sobrino, Horacio Garcia Rossi, Yvaral, Joël Stein and Vera Molnár was a collective group of opto-kinetic artists that—according to its 1963 manifesto—appealed to the direct participation of the public with an influence on its behavior, notably through the use of interactive labyrinths.

Some members of the group Nouvelle tendance (1961–1965) in Europe also were engaged in op art as Almir Mavignier and Gerhard von Graevenitz, mainly with their serigraphics. They studied optical illusions. The term op irritated many of the artists labeled under it, specifically including Albers and Stanczak. They had discussed upon the birth of the term a better label, namely perceptual art. From 1964, Arnold Schmidt (Arnold Alfred Schmidt) had several solo exhibitions of his large, black and white shaped optical paintings exhibited at the Terrain Gallery in New York.