The principal concern of this chapter is to provide those in the multimedia or content protection community with an overview of multimedia content encryption technology. Multimedia (image, audio, or video) content encryption technologies are reviewed, from the background, brief history, performance requirement, to research progress. Additionally, the general encryption algorithms are classified, and their performances are analyzed and compared. Furthermore, some special encryption algorithms are introduced. Finally, some open issues and potential research topics are presented, followed by some conclusions. The author hopes that the chapter will not only inform researchers of the progress of multimedia content encryption, but also guide the design of practical applications in the industry field.