A tracksuit is an article of clothing consisting of two parts: trousers and a jacket usually with front zipper. It was originally intended for use in sports, mainly for athletes to wear over competition clothing (such as running shirt and shorts or a swimsuit) and to take off before competition. In modern times, it has become commonly worn in other contexts. The tracksuit was one of the earliest uses of synthetic fibers in sportswear.

A descendant of the tracksuit, the shell suit, which arrived in the late 1980s, was popular with the hip hop and breakdancing scene of the era. They were manufactured from a mix of cellulose triacetate and polyester making them shiny on the outside, with distinctive combinations of colours.

Most tracksuits have a mesh interior which allows the user to wear them without any undergarment such as underwear. This is much like a bathing suit. Many people wear it for physical exercise sessions. A sauna suit is a specialized form of tracksuit made of a waterproof fabric such as coated nylon or PVC that is designed to make the wearer sweat profusely. Sauna suits are primarily used for temporary weight loss.