Riddarholmen (Swedish: "The Knights' Islet") is a small islet in central Stockholm, Sweden. The island forms part of Gamla Stan, the old town, and houses a number of private palaces dating from the 17th century. The main landmark is the church Riddarholmskyrkan, the royal burial church since the 16th century and where a number of Swedish monarchs lie buried.

The western end of the island gives a magnificent panoramic and photogenic view of the bay Riddarfjärden, often used by TV journalists with Stockholm City Hall in the background. A statue of Birger Jarl, traditionally regarded to be the founder of Stockholm, is standing on a pillar in front of the Bonde Palace north of Riddarholmskyrkan.

Other notable buildings include the Old Parliament Building in the south-eastern corner, the Old National Archive on the eastern shore, and the so called Norstedt Building, the old printing house of the publisher Norstedts, the tower roof of which is a well-known silhouette on the city's skyline.