Mariehamn is the capital of Åland, an autonomous territory under Finnish sovereignty. As of 31 January 2005 the population of Mariehamn was 10,716 — almost half of the population of Åland lives there. The area of Mariehamn municipality is 11 km².

The town, founded in 1861, was named after Marie Alexandrovna, the Empress consort of Alexander II of Russia. Its name in Finnish — as sometimes given on maps and in other Finnish-language documents — is Maarianhamina.

Mariehamn is the seat of the Government and Parliament of Åland.

Like all of Åland, Mariehamn is unilingually Swedish-speaking and around 91% of the inhabitants have Swedish as their native language.