Crystal Cubism (French: Cubisme cristal or Cubisme de cristal) is a distilled form of Cubism consistent with a shift, between 1915 and 1916, towards a strong emphasis on flat surface activity and large overlapping geometric planes. The primacy of the underlying geometric structure, rooted in the abstract, controls practically all of the elements of the artwork.

This range of styles of painting and sculpture, especially significant between 1917 and 1920 (referred to alternatively as the Crystal Period, classical Cubism, pure Cubism, advanced Cubism, late Cubism, synthetic Cubism, or the second phase of Cubism), was practiced in varying degrees by a multitude of artists; particularly those under contract with the art dealer and collector Léonce Rosenberg—Jean Metzinger, Juan Gris, Albert Gleizes, Henri Laurens, and Jacques Lipchitz most noticeably of all. The tightening of the compositions, the clarity and sense of order reflected in these works, led to its being referred to by the French poet and art critic Maurice Raynal as 'crystal' Cubism. Considerations manifested by Cubists prior to the outset of World War I—such as the fourth dimension, dynamism of modern life, the occult, and Henri Bergson's concept of duration—had now been vacated, replaced by a purely formal frame of reference that proceeded from a cohesive stance toward art and life.

As post-war reconstruction began, so too did a series of exhibitions at Léonce Rosenberg's Galerie de L'Effort Moderne: order and the allegiance to the aesthetically pure remained the prevailing tendency. The collective phenomenon of Cubism once again—now in its advanced revisionist form—became part of a widely discussed development in French culture. Crystal Cubism was the culmination of a continuous narrowing of scope in the name of a return to order; based upon the observation of the artists relation to nature, rather than on the nature of reality itself.

Crystal Cubism, and its associative rappel à l’ordre, has been linked with an inclination—by those who served the armed forces and by those who remained in the civilian sector—to escape the realities of the Great War, both during and directly following the conflict. The purifying of Cubism from 1914 through the mid-1920s, with its cohesive unity and voluntary constraints, has been linked to a much broader ideological transformation towards conservatism in both French society and French culture. In terms of the separation of culture and life, the Crystal Cubist period emerges as the most important in the history of Modernism.

Cubism, from its inception, stems from the dissatisfaction with the idea of form that had been in practice since the Renaissance. This dissatisfaction had already been seen in the works of the Romanticist Eugène Delacroix, in the Realism of Gustave Courbet, in passing through the Symbolists, Les Nabis, the Impressionists and the Neo-Impressionists. Paul Cézanne was instrumental, as his work marked a shift from a more representational art form to one that was increasingly abstract, with a strong emphasis on the simplification of geometric structure. In a letter addressed to Émile Bernard dated 15 April 1904, Cézanne writes: "Interpret nature in terms of the cylinder, the sphere, the cone; put everything in perspective, so that each side of an object, of a plane, recedes toward a central point."

Cézanne was preoccupied by the means of rendering volume and space, surface variations (or modulations) with overlapped shifting planes. Increasingly in his later works, Cézanne achieves a greater freedom. His work became bolder, more arbitrary, more dynamic and increasingly nonrepresentational. As his color planes acquired greater formal independence, defined objects and structures began to lose their identity.

Artists at the forefront of the Parisian art scene at the outset of the 20th century would not fail to notice the tendencies toward abstraction inherent in the work of Cézanne, and ventured still further. A reevaluation in their own work in relation to that of Cézanne had begun following a series of retrospective exhibitions of Cézanne's paintings held at the Salon d'Automne of 1904, the Salon d'Automne of 1905 and 1906, followed by two commemorative retrospectives after his death in 1907. By 1907, representational form gave way to a new complexity; subject matter progressively became dominated by a network of interconnected geometric planes, the distinction between foreground and background no longer sharply delineated, and the depth of field limited.

From the 1911 Salon des Indépendants, an exhibition which officially introduced "Cubism" to the public as an organized group movement, and extending through 1913, the fine arts had evolved well beyond the teachings of Cézanne. Where before, the foundational pillars of academicism had been shaken, now they had been toppled. "It was a total regeneration", writes Gleizes, "indicating the emergence of a wholly new cast of mind. Every season it appeared renewed, growing like a living body. Its enemies could, eventually, have forgiven it if only it had passed away, like a fashion; but they became even more violent when they realized that it was destined to live a life that would be longer than that of those painters who had been the first to assume the responsibility for it". The evolution towards rectilinearity and simplified forms continued through 1909 with greater emphasis on clear geometric principles; visible in the works of Pablo Picasso, Georges Braque, Jean Metzinger, Albert Gleizes, Henri Le Fauconnier and Robert Delaunay.