Inertial sensors-based systems are relatively recent. Knowledge and development of methods and algorithms for the use of such systems for clinical purposes is therefore limited, if compared with camera-based systems. However, their advantages in terms of cost effectiveness, portability, small size, are valid reasons to follow this direction. The protocols described in the book can be particularly helpful for rehabilitation centers in which the high cost of instrumentation or limitations in the working areas and specialized personnel, do not allow the use of camera-based systems. The application of inertial sensors on lower limb amputees highlights conditions which are challenging for magnetometer-based systems. A solution for solving this problem by means of a new method for improving the accuracy of the Xsens products in measuring 3D kinematics is presented. The book is a demonstration of how a strict collaboration between the industry, the clinical centers and the research laboratories can improve the knowledge, exchange know-how, with the common goal to develop new application-oriented systems.