This chapter discusses the principles of endoscopy and its applications in neurosurgery. Endoscope is an illuminated, usually fiberoptic, flexible or rigid tubular instrument for visualizing the interior of a hollow organ or a part for diagnostic or therapeutic purposes that typically has one or more channels to enable passage of instruments. Endoscope is an important tool in the neurosurgeon’s armamentarium, which provides excellent illumination and magnification. It became very popular because the intervention can be performed with minimal injury to the neural structures and less retraction. To recognize the potential applications of endoscopic neurosurgery, one can consider the impact created by the endoscopy in the other medical and surgical subspecialties. Multiple diagnostic and therapeutic procedures are performed routinely using devices such as arthroscopes, bronchoscopes, cystoscopes, colonoscopes, laparoscopes, etc.