La materia granular o materia granulada es aquella que está formada por un conjunto de partículas macroscópicas sólidas lo suficientemente grandes para que la fuerza de interacción entre ellas sea la de fricción. Colectivamente, este tipo de materia presenta propiedades que pueden semejar, dependiendo del tipo de fuerzas a las que esté sometida, a las del estado sólido, el estado líquido o un gas. Una característica importante es que la materia granular tiende a disipar rápidamente la energía de sus partículas debido a la fuerza de fricción. Esto da lugar a fenómenos de gran importancia como las avalanchas, los atascamientos en descargas de silos, entre otras. Como ejemplos de materia granular se encuentran los granos y semillas, la nieve, la arena, etc. Aunque la materia granular es conocida desde la antigüedad, la aparición de fenómenos que aparentan ir en contra de la intuición, como el efecto de las nueces del Brasil, ha hecho que en los últimos años se haya incrementado su estudio por parte de los físicos. El estudio de este tipo de materiales es de suma importancia debido a que es el tipo de materia más utilizada por el hombre solamente después del agua.

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A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations. Thus, the lower size limit for grains in granular material is about 1 µm. On the upper size limit, the physics of granular materials may be applied to ice floes where the individual grains are icebergs and to asteroid belts of the Solar System with individual grains being asteroids. Some examples of granular materials are snow, nuts, coal, sand, rice, coffee, corn flakes, fertilizer and ball bearings. Powders are a special class of granular material due to their small particle size, which makes them more cohesive and more easily suspended in a gas. Granular materials are commercially important in applications as diverse as pharmaceutical industry, agriculture, and energy production. Research into granular materials is thus directly applicable and goes back at least to Charles-Augustin de Coulomb, whose law of friction was originally stated for granular materials. The soldier/physicist Brigadier Ralph Alger Bagnold was an early pioneer of the physics of granular matter and whose book The Physics of Blown Sand and Desert Dunes remains an important reference to this day. According to material scientist Patrick Richard, "Granular materials are ubiquitous in nature and are the second-most manipulated material in industry (the first one is water)". In some sense, granular materials do not constitute a single phase of matter but have characteristics reminiscent of solids, liquids, or gases depending on the average energy per grain. However, in each of these states granular materials also exhibit properties which are unique. Granular materials also exhibit a wide range of pattern forming behaviors when excited (e.g. vibrated or allowed to flow). As such granular materials under excitation can be thought of as an example of a complex system.

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