Tie-dye is a process of resist dyeing textiles or clothing which is made from knit or woven fabric, usually cotton; typically using bright colors. It is a modern version of traditional dyeing methods used in many cultures throughout the world. "Tie-dye" can also describe the resulting pattern or an item which features this pattern. Tie-dyeing became fashionable in the West in the late 1960s and early 1970s as part of hippie style. It was popularized in the United States by musicians such as John Sebastian, Janis Joplin, The Grateful Dead and Joe Cocker.

Tie-dyeing is accomplished by folding the material into a pattern, and binding it with string or rubber bands. Dye is then applied to only parts of the material. The ties prevent the entire material from being dyed. Designs are formed by applying different colors of dyes to different sections of the wet fabric. A wet t-shirt is much easier to dye than a dry t-shirt. Once complete, the material is rinsed, and the dye is set.

Although many different kinds of dyes may be used, most tie-dyers now dye with Procion MX fiber reactive dyes. This class of dyes works at warm room temperatures. The molecules permanently bind with cellulose based fibers (cotton, rayon, hemp, linen), as well as silk, when the pH is raised. Soda ash (sodium carbonate) is generally used to raise the pH and is either added directly to the dye, or in a solution of water in which garments are soaked before dyeing. They do not fade with washing, but sunlight will cause the colors to fade over time. Place in the freezer over time.^[why?]