Seersucker, hickory stripe or railroad stripe is a thin, puckered, cotton fabric, usually striped or chequered, used to make clothing for hot weather. The word originates from the Persian words شیر shîr and شکر shakar, literally meaning "milk and sugar", from the gritty texture ("sugar") on the otherwise smooth ("milk") cloth. This lightweight silk originated in India and was introduced to the wider world from there. Seersucker is woven in such a way that some threads bunch together, giving the fabric a wrinkled or puckered appearance. This effect is often achieved during weaving by feeding the warp threads for the puckered bands at a greater rate than the warp threads of the smooth stripes. (These are often of different colors but do not need to be.) The unevenness causes the fabric to be mostly held away from the skin rather than being plastered on it when wet with sweat, facilitating heat dissipation and air circulation. It also means that ironing is not necessary.

Common items made from seersucker include suits, shorts, shirts, dresses, and robes. In the United States, it is often made in white and blue stripes; however, it is produced in a wide variety of colors, usually with narrow plain and puckered stripes in different colors.

Seersucker originated in colonial India, taking its name from the Persian phrase shir o shekar, meaning 'milk and sugar,' referring to its mix of smooth and rough textures. At the time, it was valued as a workingman’s fabric. It was first made in the Indian subcontinent from where this fabric was exported to the European market in 17th century. English and French textile manufacturers quickly took it on and started their own production. In the 18th century the fabric was exported to the American colonies. It was durable and used in cool curtains, mattress covers, and work clothing.

Worn from the 19th century by the Spanish Army in the Philippines and later Morocco, it was known to them as rayadillo. During the British colonial period, seersucker was also a popular material in Britain's hot-weather colonies such as British India. When seersucker was introduced in the United States it was used for many garments. For suits, the material was considered a mainstay of the summer wardrobe of gentlemen, especially in the hot and humid South before air conditioning.

During the American Civil War, this material was used to make cheap but durable haversacks and some uniform items, such as the famous baggy pants of Confederate Zouaves such as the Louisiana Tigers. From the mid-Victorian era until the early 20th century, seersucker was also known as bed ticking due to its widespread use in mattresses, pillow cases and nightshirts during the hot summers in the Southern US and Britain's overseas colonies.

The fabric was originally worn by the poor in the U.S. until preppy undergraduate students began wearing it in the 1920s in an act of reverse snobbery.

Seersucker's comfort and easy laundering made it the choice of Captain Anne A. Lentz for the summer service uniforms of the first female United States Marines. Lentz was one of the first female officers selected to run the Marine Corps Women's Reserve during the Second World War. From the 1940s onwards, nurses and US hospital volunteers also wore uniforms made from a type of red and white seersucker known as candy stripe.

In the days of the Old West, a type of heavyweight indigo or navy blue seersucker known as hickory stripe was used to make the overalls, work jackets and peaked caps of train engineers and railroad workers such as George "Stormy" Kromer and Casey Jones. It was later worn by butchers and employees of the gasoline companies, most notably Standard Oil.