Though system control methods for 3D UIs have been developed and used extensively, many issues are still open for further research. We have discussed a wide range of techniques, but the design space for such techniques is virtually limitless. We expect to see many new and interesting 3D system control techniques, not only within the categories described here but also in new categories that have not yet been invented. There is also a lack of good empirical evidence for the user experience of various system control techniques at the present time—further UX evaluations are needed in order to validate current design guidelines and develop new ones. Nevertheless, this chapter has served to demonstrate the importance and complexity of system control interfaces and has presented a wide range of existing system control techniques for 3D UIs. This concludes our tour through 3D interaction techniques for the universal tasks. We now move on to general design and evaluation of 3D UIs in part V.