Divisionism, also called chromoluminarism, is the characteristic style in Neo-Impressionist painting defined by the separation of colors into individual dots or patches that interact optically.

By requiring the viewer to combine the colors optically instead of physically mixing pigments, Divisionists believed that they were achieving the maximum luminosity scientifically possible. Georges Seurat founded the style around 1884 as chromoluminarism, drawing from his understanding of the scientific theories of Michel Eugène Chevreul, Ogden Rood and Charles Blanc, among others. Divisionism developed along with another style, Pointillism, which is defined specifically by the use of dots of paint and does not necessarily focus on the separation of colors.

Divisionism is the technique of painting separate dots or patches of different colors in close proximity that interact optically in the viewer's perception to generate more luminous colors. The paints are not actually mixed but viewed close together, so the separate colors of light reflected by the paints mixes in the eye and brain; the process is called additive mixing and is also used by computer monitors. This is different from mixing different paints together to produce a new color by subtractive mixing, which is also how laser printers produce colors. Despite the theory, Seurat's paintings don't actually use true additive mixture, since the colors reflected by his paints as he used them don't actually mix in the eye. Instead, Seurat used highly contrasting colors in close proximity, but not close enough to mix additively; this effect is called simultaneous contrast, which creates a mild shimmering appearance and slightly increases the colors' apparent visual intensity.

Impressionism originated in France in the 1870s, and is characterized by the use of quick, short, broken brushstrokes to accurately capture the momentary effects of light and atmosphere in an outdoor scene. The Impressionists sought to create an "impression" of a momentary scene as perceived by the viewer, rather than a mechanically precise replication of the scene. Divisionism, also known as Pointillism, developed from Impressionism in the 1880s. The Divisionists used a technique of placing small, distinct dots of color next to one another on the canvas, rather than mixing the colors on the palette. This created a more vibrant and dynamic effect, but also required a higher level of skill and precision. Neo-Impressionism emerged in the late 19th century, used more precise and geometric shapes to build compositions and was strongly influenced by the scientific study of color theory and optical color effects, to create a more harmonious and luminous painting.

Scientists or artists whose theories of light or color had some impact on the development of Divisionism include Charles Henry, Charles Blanc, David Pierre Giottino Humbert de Superville, David Sutter, Michel Eugène Chevreul, Ogden Rood and Hermann von Helmholtz.

Divisionism, along with the Neo-Impressionism movement as a whole, found its beginnings in Georges Seurat's masterpiece, A Sunday Afternoon on the Island of La Grande Jatte. Seurat had received classical training at the École des Beaux-Arts, and, as such, his initial works reflected the Barbizon style. In 1883, Seurat and some of his colleagues began exploring ways to express as much light as possible on the canvas. By 1884, with the exhibition of his first major work, Bathers at Asnières, as well as croquetons of the island of Île de la Jatte, his style began taking form with an awareness of Impressionism, but it was not until he finished La Grande Jatte in 1886 that he established his theory of chromoluminarism. In fact, La Grande Jatte was not initially painted in the Divisionist style, but he reworked the painting in the winter of 1885–86, enhancing its optical properties in accordance with his interpretation of scientific theories of color and light.

Charles Blanc's Grammaire des arts du dessin introduced Seurat to the theories of color and vision that would inspire chromoluminarism. Blanc's work, drawing from the theories of Michel Eugène Chevreul and Eugène Delacroix, stated that optical mixing would produce more vibrant and pure colors than the traditional process of mixing pigments. Mixing pigments physically is a subtractive process with cyan, magenta and yellow being the primary colors. On the other hand, if colored light is mixed together, an additive mixture results, a process in which the primary colors are red, green and blue.

In Divisionist color theory, artists interpreted the scientific literature through making light operate in one of the following contexts: