Mariehamn (/məˈriːəhɑːmən/ mə-REE-ə-hah-mən, Finland Swedish: [mɑriːeˈhɑmn] ^ⓘ; Finnish: Maarianhamina [ˈmɑːriɑnˌhɑminɑ]; Latin: Portus Mariae) is the capital of Åland, an autonomous territory under Finnish sovereignty. The city is the seat of the Government of Åland and the Parliament of Åland, and about 40% of Åland’s population live there. Mariehamn borders Jomala to the north and west and Lemland to the east.

Like the rest of Åland, the city is unilingually Swedish-speaking. Most inhabitants have Swedish as their native language.

The coat of arms of Mariehamn reflects the city’s main livelihood, maritime transport, and its linden tree–lined parks. The coat of arms was designed by Nils Byman and confirmed in 1951.

Mariehamn’s central location in the Baltic Sea makes it a popular summer destination. Approximately 1.5 million tourists visit each year.

Mariehamn was named after the Russian empress Maria Alexandrovna (1824–1880), meaning lit. 'Marie's Port'. The town was founded on 21 February 1861 around the village of Övernäs, then part of Jomala municipality. The city later expanded into Jomala. It was built to a regular plan that remains well preserved. One of the oldest streets is Södragatan, with 19th-century wooden houses.

In the mid-19th century, cargo shipping developed, and several shipowners and shipyards settled in the growing town.

After the First World War, Mariehamn hosted the Mariehamn Grain Fleet.

On 8 November 1963, a plane crash in Mariehamn killed 22 of 25 people, Finland’s second-deadliest air accident.