Ragnarök Online often referred to as RO, is a massive multiplayer online role-playing game based on the manhwa Ragnarok by Lee Myung-jin.

Player characters exist in a world with a player environment that gradually changes with the passage of time. Major changes in the features and history of the world take place as episodes in the RO timeline. Player characters interact in a 3D environment but are represented by 2D character sprites for front, back, side and diagonal facings.

The major types of server-supported gameplay are Player vs Environment, Guild vs Guild, Player vs Player. Also supported by the game server are Group vs Group, Arena Combat, Player vs Monster, Player vs All, and various other specific scenarios at designated instance locations in the game world. NPC-run challenges and contests are also available with prizes, awards, and/or listing in a specific hall of fame listing.