染料是有颜色的物质。但有颜色的物质并不一定是染料。作为染料，必须能够使一定颜色附着在纤维上。且不易脱落、变色。染料通常溶于水中，一部份的染料需要媒染剂使染料能黏著于纤维上。

染料和色素吸收部份波长的光，所以看起来带有颜色。与染料比较，色素并不溶于水中，亦不会附著于其他物质上。

考古数据显示，染色技术于印度和中东已有超过五千年历史。当时的染料从动植物或矿物质而来，甚少经过处理。大多数染料来自植物界（如植物的根、莓类、树皮、叶子和木料等），但此类染料甚少被广泛用于商业上。

第一种人造的有机染料苯胺紫（mauveine）由威廉·珀金（William Henry Perkin）于一八五六年发明。其后共有上千种染料被发明出来。

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber.

Both dyes and pigments are colored because they absorb some wavelengths of light more than others. In contrast to dyes, pigments are insoluble and have no affinity for the substrate. Some dyes can be precipitated with an inert salt to produce a lake pigment, and based on the salt used they could be aluminum lake, calcium lake or barium lake pigments.