This chapter introduces interaction mechanisms that may not have a counterpart in the physical world. Section 10.1 introduces general motor learning and control concepts. The most important concept is remapping, in which a motion in the real world may be mapped into a substantially different motion in the virtual world. This enables many powerful interaction mechanisms. The task is to develop ones that are easy to learn, easy to use, effective for the task, and provide a comfortable user experience. Section 10.2 discusses how the user may move himself in the virtual world, while remaining fixed in the real world. Section 10.3 presents ways in which the user may interact with other objects in the virtual world. Section 10.4 discusses social interaction mechanisms, which allow users to interact directly with each other. Section 10.5 briefly considers some additional interaction mechanisms, such as editing text, designing 3D structures, and Web browsing.