Technology and computers are omnipresent in our daily lives today, in which they play a decisive role, even if they are often invisible, seamlessly integrated into our surrounding and the objects we use every day. Image-guided therapy is certainly not an exception to this. Nowadays practically all imaging devices rely on computer support, commonly used for the purpose of controlling medical devices, for post-processing acquired raw data to turn them into images, and for transmitting resulting digital data for storage or further use. Furthermore, many therapeutic devices are equipped with sophisticated sensors and actuators, which are also controlled by computers. Indeed, software support today is an intrinsic component of all phases of therapy. In this chapter, we provide an overview of tools and technologies that are used as the building blocks of almost every computational support system in image-guided therapy. The tools introduced in this chapter include segmentation, registration, localization, simulation, model generation, visualization, robotic tools, and manmachine interfaces. The use of such tools in preoperative planning and intraoperative surgical support is then described and exemplified on typical treatment scenarios.