Riddarholmen, literally The Knights Islet, is an small island in the center of Stockholm, Sweden. The island forms part of Gamla Stan, the old town, and houses a number of private palaces from the 17th century. The main attraction of Riddarholmen is the church, Riddarholmskyrkan, which served as the royal burial church since the 16th century and where a number of Swedish monarchs lie consecrated.

The palaces of Wrangel, Hessenstein, and Schering Rosenhane are today used by Svea Hovrätt, the appelate court for Svealand, while the Supreme Court and the Government Court resides in the palaces of Bonde and Stenbock respectively. Some of the older Swedish Government Agencies, like the Chamber College and the Chancellor of Justice, are also located on the island.

The western end of the island gives a magnificent open photogenic view of Riddarfjärden, often used by TV journalists with Stockholm City Hall in the background. A statue of Birger Jarl, the traditional founder of Stockholm, stands on a pillar in front of the Bonde Palace to the north of Riddarholmskyrkan.

The oldest recorded name for the island is Kidaskär. When a Greyfriars monastery was built in the 13th century, the name changed to Gråmunkeholmen, Greyfriar's islet. During the Protestant Reformation the monastery was closed down and converted into a church, and in 1638 the island acquired its present name.