Mariehamn ( 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. Mariehamn is the seat of the Government and Parliament of Åland, and 40% of the population of Åland live in the city. It is mostly surrounded by Jomala, the second-largest municipality in Åland in terms of population; to the east, it is bordered by Lemland. Like the rest of Åland, Mariehamn is unilingually Swedish-speaking and around 81% of the inhabitants speak it as their native language.

The theme of the coat of arms of Mariehamn refers to the city's main livelihood, maritime transport, and the city's parks, which are typically lined with linden trees. The coat of arms was designed by Nils Byman and confirmed in 1951.

Due to its central location in the Baltic Sea, Mariehamn has become a major summer resort town for global tourism; as many as 1.5 million tourists visit annually.