Revision with unchanged content. In abdominal surgery, laparoscopic ultrasound is widely used for minimally invasive procedures. Because of the missing visual feedback, it is often difficult for the surgeons to relate the ultrasound transducer to patient anatomy and images. Instrument tracking techniques for navigation and visualization can provide great benefits. Electromagnetic systems are the only currently available means to determine the pose of the transducer tip inside the patient, but the electromagnetic field can be distorted, leading to erroneous measurements. The author Tobias Reichl presents two new methods for online error detection and correction for the tracking of flexible laparoscopic ultrasound probes. With hybrid magneto-optic tracking, deviations between optical and electromagnetic tracking are used to estimate the tracking error at the transducer tip. The second approach involves a mathematical model of the movements of the flexible transducer tip. Both methods were rigorously tested in experiments and comprehensively evaluated in comparison to related work. This book is addressed to professionals in education, research, and development for computer aided surgery and medical augmented reality.