Kustavi (; Swedish: Gustavs) is a municipality of Finland. It is in the province of Western Finland and is part of the Southwest Finland region. The municipality has a population of and covers an area of km2 of which km2 is water. The population density is PD/km2. There are over 2,000 isles within the municipal area. The municipality is a very popular summer resort and contains over 2,800 summer cottages. The population increases tenfold during the summer months. The larger events are Volter Kilpi literature week in July and Salmon market (Lohimarkkinat) in August. The basic services of the municipality include 3 groceries, a liquor store, a library and a bank. There are two ferry connections to Brändö and Iniö. The municipality is unilingually Finnish even though it is located adjacent to the Swedish speaking Åland-region.
