The sleeping car or sleeper (often wagon-lit) is a railway passenger car that can accommodate all passengers in beds of one kind or another, for the purpose of sleeping. George Pullman was the main American innovator and owner of sleeper cars in the late 19th and early 20th centuries when railroads dominated intercity passenger travel.

The first such cars saw sporadic use on American and English railways in the 1830s; they could be configured for coach seating during the day.

Possibly the earliest example of a sleeping car (or bed carriage, as it was then called) was on the London & Birmingham and Grand Junction Railways between London and Lancashire, England. The bed carriage was first made available to first-class passengers in 1838.

In the spring of 1839, the Cumberland Valley Railroad pioneered sleeping car service in the United States with a car named "Chambersburg", between Chambersburg, Pennsylvania and Harrisburg, Pennsylvania. A couple of years later a second car, the "Carlisle", was introduced into service.

In 1857, the Wason Manufacturing Company of Springfield, Massachusetts – one of the United States' first makers of railway passenger coach equipment – produced America's first specifically designed sleeping car. Canadian railways soon followed with their own sleeping cars: first the Grand Trunk in 1858, then the Great Western. The Great Western's sleeping cars were manufactured in-house, with the first three built in 1858, and the railway operating six by 1863.

The man who ultimately made the sleeping car business profitable in the United States was George Pullman, who began by building a luxurious sleeping car (named Pioneer) in 1865. The Pullman Company, founded as the Pullman Palace Car Company in 1867, owned and operated most sleeping cars in the United States until the mid-20th century, attaching them to passenger trains run by the various railroads; there were also some sleeping cars that were operated by Pullman but owned by the railroad running a given train. During the peak years of American passenger railroading, several all-Pullman trains existed, including the 20th Century Limited on the New York Central Railroad, the Broadway Limited on the Pennsylvania Railroad, the Panama Limited on the Illinois Central Railroad, and the Super Chief on the Atchison, Topeka and Santa Fe Railway.

Pullman cars were normally a dark "Pullman green", although some were painted in the host railroad's colors. The cars carried individual names, but usually did not carry visible numbers. In the 1920s, the Pullman Company went through a series of restructuring steps, which in the end resulted in a parent company, Pullman Incorporated, controlling the Pullman Company (which owned and operated sleeping cars) and the Pullman-Standard Car Manufacturing Company. Due to an antitrust verdict in 1947, a consortium of railroads bought the Pullman Company from Pullman Incorporated, and subsequently railroads owned and operated Pullman-made sleeping cars themselves. Pullman-Standard continued manufacturing sleeping cars and other passenger and freight railroad cars until 1980.

For nearly a year during the end of World War II the United States government banned sleeping cars for runs of less than 450 miles (720 km) in order to make sleepers available for transporting troops returning to the US from Europe, many being deployed in the Pacific Theater. The development of the Interstate Highway System in the 1950s and the expansion of jet airline travel in the same decade negatively affected train travel.