Image guided orthopedic intervention has seen rapid development in the past two decades. In many applications, the intraoperative use of medical imaging data has increased the safety and robustness of the surgical outcome. However it has also increased the applied radiation dose. Navigation systems were introduced in order to reduce the invasiveness of such procedures, while increasing the accuracy and safety of the procedures. The clinical procedures are often complex. Newly introduced systems often add more complexity and are not smoothly integrated into the clinical workflow. This book introduces two new concepts for computer aided surgery. Based on these concepts, it proposes innovative solutions satisfying the application specific requirements of the exemplary applications in computer assisted spine surgery. The concepts discussed use augmented reality visualization techniques. The first solution is based on head mounted displays for the visualization of 3D imaging data. The second approach is an extension of a mobile C-arm that is used for X-ray imaging in the operation room.