The objective of this proposal is to reduce the invasiveness and increase the safety of surgical procedures at the skull base by introducing a new robotic system for natural orifice skull base surgery. Despite compelling patient benefits compared to highly invasive transfacial and transcranial approaches, the endonasal approach - in which surgical instruments are deployed to the skull base through a nostril and the nasal cavities - is only used in a small percentage of cases due to limitations in current surgical instrumentation. The proposed system aims to remedy this through a new kind of surgical robot with needle-diameter, tentacle-like instruments. It will be able to transport surgical tools and cameras along curvilinear paths and work around corners (e.g. enable physicians to resect tumors by curving around the carotid arteries), while providing the physician with a comfortable and intuitive control interface conceptually similar to that of the da Vinci Surgical System. Such a robot, with instruments made using concentric, curved, elastic tubes, has the potential to profoundly impact public health because: (1) incidence is high - 15-20% of all primary brain tumors occur in the pituitary and 1 in 5 people will develop one, with 1 in 120 requiring skull base surgery (>1cm tumor); (2) traditional approaches are highly invasive - they require either deconstruction of facial tissue and bone, or a craniotomy and associated trauma to the brain; and (3) there exists an underutilized, yet clinically proven alternative - the endonasal approach, which is not more widely deployed due to the difficulty of accomplishing it using conventional surgical tools. The proposed system will be developed through three Specific Aims. Aim 1 involves measuring surgical forces and geometry and using this information with mechanics models to optimally design the proposed robotic system. Aim 2 addresses developing control, force feedback, and assistance algorithms for the surgeon, together with visual displays showing endoscope images, registered preoperative medical images, and robot instrument locations. Magnetic tracking will enable force sensing and enhance the accuracy of surgical navigation. Aim 3 consists of experiments designed to evaluate robot performance in reaching surgically relevant locations, and in removing tissue in laboratory settings, in skull phantoms, and in cadaver studies. The final objective of this R01 is a fully functional robotic system with al the components necessary for operating room use, to assist the surgeon in natural orifice (i.e. transnasal) skull base surgery.