The term endoscopic Neurosurgery is used basically for all procedures that are performed with the help of endoscopes. Endoscopic procedures may be performed purely endoscopic, for example for the treatment of occlusive hydrocephalus and cystic lesions or in combination with the operating microscope for example for the treatment of large tumors of the skull base or vascular lesions. The latter technique is named endoscope-assisted microsurgery (EAM). If endoscopes are used as the only optical tool but manipulations performed along the scope, it is referred to as endoscope-controlled microsurgery (ECM). This technique is recently more and more applied for transnasal skull base surgery.