Dye is a chemical substance used to impart color to various materials such as textiles, paper, leather, and other materials, such that the coloring is not readily altered by washing, heat, light, or other factors to which the material is likely to be exposed. Dyes differ from pigments, which are finely ground solids dispersed in a liquid, such as paint or ink, or blended with other materials. Most dyes are organic compounds, meaning they contain carbon, whereas pigments may be inorganic compounds or organic compounds.

Dyes can be natural or synthetic, and they are classified based on their chemical structure and the type of fibers they are used on. Some common types of dyes include direct, azoic, vat, sulfur, and reactive dyes. The color of a dye is dependent upon the ability of the substance to absorb light within the visible region of the electromagnetic spectrum (380-750 nm) .

Dyes are made by taking naturally occurring colorants and converting them into a soluble form that can be used in several ways. This can be done through different methods, but almost all of them depend on chemical bonding to ensure that no dye is wasted. The affinity of a dye for a fabric depends on the chemical structure of the dye and fabric molecules and on the interactions between them. Chemical bonding thus plays an important role in how and why dyes work.

Dyes have various uses, including coloring textiles, paper, leather, and other materials, as well as indicators, biological stains, fire retardants, pigments, antioxidants, and pharmaceuticals.