The Stockholm archipelago (Swedish: Stockholms skärgård) is the largest archipelago in Sweden, and the second-largest archipelago in the Baltic Sea (the largest being across the Baltic in Finland).
The archipelago extends from Stockholm roughly 60 kilometres (37 mi) to the east. In a north–south direction, it mainly follows the coastline of the Södermanland and Uppland provinces, reaching roughly from Öja island, south of Nynäshamn, to Väddö, north of Norrtälje. It is separated from Åland by a stretch of water named South Kvarken. A separate group of islands lies further north, near the town of Öregrund. There are approximately 30,000 islands and islets. Some of the better-known islands are Dalarö, Finnhamn, Nässlingen, Grinda, Husarö, Ingarö, Isö, Ljusterö, Möja, Nämdö, Rödlöga, Tynningö, Utö, Svartsö and Värmdö.
The biggest towns of the archipelago, apart from Stockholm, are Nynäshamn, Vaxholm and Norrtälje. The village of Ytterby, famous among chemists for naming no fewer than four chemical elements (erbium, terbium, ytterbium and yttrium), is situated on Resarö in the Stockholm archipelago.
The shipping routes from the Baltic to Stockholm pass through the archipelago. There are three main entrances suitable for deep-draught craft, namely, those near Landsort, Sandhamn, and Söderarm.