A troopship (also troop ship or troop transport) is a ship used to carry soldiers, either in peacetime or wartime. Operationally, troopships are normal ships, and unlike landing ships, cannot land troops directly on shore, typically loading and unloading at a seaport.

Originally regular naval vessels were used to carry troops overseas, typically in an ad hoc fashion. During the Napoleonic Wars, the French built a fleet of 2,000 special-purpose barges as part of a plan to invade Britain, but these were never used. In the 20th century, navies began to charter civilian ocean liners, painting them gray and giving them minimal armament; their speed, originally intended to minimize travel time, was valuable for outrunning submarines. Navies also built dedicated transports of lesser performance, protecting them by operating them in convoys.

The RMS Queen Mary and the RMS Queen Elizabeth were two of the most famous converted liners of World War II. When they were fully optimized, each of them could carry well over 10,000 troops per trip. In the era of the Cold War the United States designed the SS United States so that it could easily be converted from a liner to a troopship, in case of war. More recently, RMS Queen Elizabeth 2 carried 3000 troops to the Falklands War.

By the end of the century, nearly all long-distance transfers of soldiers were being done by air.