Trelleborg (Swedish pronunciation: [trɛlɛˈbɔrj]) is a town in Skåne County, Sweden, with 43,359 inhabitants as of 31 December 2015. It is the southernmost town in Sweden located some 10–15 kilometres (6.2–9.3 mi) west from the southernmost point of Sweden and the Scandinavian Peninsula. It is one of the most important ferry towns in Scandinavia as well as around the Baltic Sea, and the main town of the Söderslätt agricultural areas.

The first written record of the name is from 1257, Threlæburgh. The name is found in many places in Scandinavia. Borg means castle or stronghold and träl can mean thrall, but can also refer to the leaning poles on the outside of the medieval Viking stronghold. Remains of the original stronghold were excavated in 1988.

The name may also have originated from the stronghold that still remains in the center of the city. Strongholds like that have been found at several places around Scandinavia, mostly in the south of Sweden and Denmark, and are all called trelleborgs. The name is likely to have originated from that borg.

The earliest written record of Trelleborg is from 1257. Three years later Trelleborg was presented as a wedding gift from the Danish royal family to the Swedish Prince Valdemar. It was soon reconquered by the Danes, and continued to belong to Denmark until 1658, when Scania was lost to Sweden by the Treaty of Roskilde.

In medieval times, Trelleborg had an important part in herring fishing. At that time, this was conducted along the entire coastline of what is now Sweden, as the herring shoals were of such great numbers that fishermen were said to have been able to stand on the shore and land fish with nets. Trelleborg became an important merchant city as merchants from Germany came to trade herring. In 1619 following a devastating fire, the Danish King decided that one merchant city on the coast was sufficient and revoked Trelleborg's status as a merchant city in favour of Malmö.

Not until 1840 was Trelleborg allowed to become a merchant city, and not until 1867 did it regain its rights as a city of Sweden. Mostly this was thanks to the work of a few stubborn men, who had continuously been petitioning the Swedish Riksdag with these requests since 1658.

In 1962, in Trelleborg, a group of Macedonian political emigrants founded the Movement for the Liberation and Unification of Macedonia.

The local government reform of 1971 made Trelleborg the seat of Trelleborg Municipality, covering both rural and urban areas.