A T-shirt (also spelled tee shirt, or tee for short) is a style of fabric shirt named after the T shape of its body and sleeves. Traditionally, it has short sleeves and a round neckline, known as a crew neck, which lacks a collar. T-shirts are generally made of stretchy, light, and inexpensive fabric and are easy to clean. The T-shirt evolved from undergarments used in the 19th century and, in the mid-20th century, transitioned from undergarments to general-use casual clothing.

They are typically made of cotton textile in a stockinette or jersey knit, which has a distinctively pliable texture compared to shirts made of woven cloth. Some modern versions have a body made from a continuously knitted tube, produced on a circular knitting machine, such that the torso has no side seams. The manufacture of T-shirts has become highly automated and may include cutting fabric with a laser or a water jet.

T-shirts are inexpensive to produce and are often part of fast fashion, leading to outsized sales of T-shirts compared to other attire. For example, two billion T-shirts are sold worldwide per year, and the average person in Sweden buys nine T-shirts a year. Production processes vary but can be environmentally intensive and include the environmental impact caused by their materials, such as cotton, which uses a lot of water and pesticides.