This chapter covers the topic of multiplayer serious games. Multiplayer games are discussed in terms of game types and forms, genres and techniques, as well as their impact on the use of multiplayer games. Based on that, this chapter will show how different types of multiplayer genres and techniques can be used for various serious game purposes. This chapter further provides an introduction to ... [Show full abstract] the topic of collaborative learning and collaborative multiplayer games—and their use for game-based collaborative learning. We discuss how collaborative learning concepts are inherently used by some massive multiplayer online games, and how those concepts can be used more thoroughly by using the multiplayer paradigm for game-based collaborative learning. Further, it is shown how various multiplayer design aspects like number of players, persistency, matchmaking, interaction, or social aspects need to be considered in the design phase of a multiplayer game.