Coordinates: 60°18′N 21°00′E / 60.3°N 21°E / 60.3; 21

Archipelago Sea (Finnish Saaristomeri, Swedish Skärgårdshavet) is a part of the Baltic Sea between the Gulf of Bothnia, the Gulf of Finland and the Sea of Åland, within Finnish territorial waters. By some definitions it contains the largest archipelago (island group) in the world by the number of islands, although many of the islands are very small and tightly clustered.

The larger islands are inhabited and connected by ferries and bridges. The Åland Islands, including the largest islands of the region, form an autonomous region within Finland. The rest of the islands are part of Finland Proper. The Archipelago Sea is a significant tourist destination.

The Archipelago Sea covers a roughly triangular area with the cities of Mariehamn (60°5′52″N 19°56′23″E / 60.09778°N 19.93972°E / 60.09778; 19.93972), Uusikaupunki (60°48′4″N 21°24′50″E / 60.80111°N 21.41389°E / 60.80111; 21.41389), and Hanko (59°50′0″N 22°58′15″E / 59.833333°N 22.97083°E / 59.833333; 22.97083), at the corners. The archipelago can be divided into inner and outer archipelagos, with the outer archipelago consisting mainly of smaller, uninhabited islands. The total surface area is 8300 square kilometers, of which 2000 square kilometers is land.