This volume in the Robotic Radiosurgery series is devoted to the theory and practice in the emerging field of stereotactic radiosurgery for extracranial tumors, particularly those that move as patients breathe. Special attention is given to the frameless robotic radiosurgery device known as the CyberKnife. Moving tumors are treated with the CyberKnife using a revolutionary new tool, called the Synchrony® Respiratory Tracking System, which can track moving tumors in real time. Detailed information is provided on the technology and methodology for delivery of high doses of radiation to moving targets, radiobiological and radiological principles, and the challenges faced by clinicians performing extracranial stereotactic radiosurgery. Furthermore, there are thorough reviews of the general clinical literature on stereotactic radiation treatment of tumors of the lungs, liver, and pancreas, and the latest clinical data from clinicians conducting clinical studies using the CyberKnife® Robotic Radiosurgery System.