Karlshamn (Swedish pronunciation: [ˈkɑ̂ːɭshamn]) is a locality and the seat of Karlshamn Municipality in Blekinge County, Sweden. It had 13,576 inhabitants in 2015, out of 31,846 in the municipality.

Karlshamn received a Royal Charter and city privileges in 1664, when King Charles X Gustav, in Swedish Karl, realized the strategic location near the Baltic Sea. In 1666 the town was named Karlshamn, meaning Karl's Port in honour of the Swedish king.

At the outlet of the stream Mieån was found a harbour and fishing village "Bodekull" and a farm "Bodetorp". In the lower parts of "Mörrumsån" was a prosperous salmon fishery.

Sweden gained supremacy over the territory through Treaty of Roskilde 1658. The king Charles X Gustav immediately inspected the coast and found here a tremendously beautiful and incomparable harbour. Fortifications designed by Erik Dahlberg were erected on Boön 1659 and on Friesholmen 1675, called "Kastellet". Troops loyal to the Danish king attacked the town twice in 1676–78. The location attracted foreign merchants and in 1664 royal privileges were issued to establish a town named after the king, meaning "Karl's Port". The settlement expanded rapidly to count 647 citizens in the year 1700. Pestilence reduced the population in 1710.

Industries based on agricultural and mineral products were established during the 18th century. A fire of 1763 destroyed the northern part of the town, another fire ravaged in 1790. The intercontinental war of 1810 gave Karlshamn a rare possibility to trade goods and the citizens prospered. Punch, tobacco and snuff powder were produced in town. Craftsmanship was common until circa 1880, when industrial production took over. The town had 6529 citizens by 1883, the town plan covered 63 hectares and buildings were erected on 693 plots. The railway inaugurated in 1874 connected Karlshamn to Vislanda in the northern province. 1890, the coastal railroad was built. 1876, L.O. Smith established production of aquavit in the town and built a new distillery in 1884 which was effective until 1893, whereafter it was converted into a sugar refinery. In 1912 was established production of vegetable oil in the old refinery, a still continuing operation under the label AAK. Stone cutting in granite quarries was a heavy export industry circa 1850–1940. In Mörrum a paper mill was built in 1962. Since 1975 the port of Karlshamn has gradually transferred its operations to the Stilleryd location, west of town. 1965 was a new hospital building in operation.

Karlshamn is considered to situate in strategically sensitive area, about 50 kilometres from the Swedish main naval base at Karlskrona. Gazprom would lease Karlshamn's port to construct Nord Stream 2 gas pipeline after the national government dropped its objections.

Karlshamn has an oceanic climate typical of Southern Sweden, with relatively mild winters for the latitude and summers that are relatively warm. It is influenced by its southerly position on the coastline, which causes particularly mild autumn average temperatures as the maritime influence moderates the cooling. The precipitation pattern is highly variable from year to year depending on prevailing wind patterns.

University
In Karlshamn a branch of the Blekinge Institute of Technology (BTH) was established in 2000. It focuses on media technology, such as digital games, digital visual production, digital audio production and interactions with web technologies.
Secondary Schools
The upper secondary school (grade 10 to 13) is Väggaskolan in Karlshamn. There are many primary schools (grade 0-9) in the boroughs.