Endoscopy has been adopted for transsphenoidal pituitary surgery. A rigid rod-lens endoscope, 4-mm in diameter and 18 cm in length, is used in replacement of the operating microscope. This endoscopic technique utilizes the patient's natural nasal air passage as a surgical corridor without a sublabial or nasal mucosal incision. The use of a transsphenoidal retractor is not necessary. Postoperative nasal packing is not required. The average length of a patient's hospital stay is overnight. Postoperative discomfort is minimal. An angled lens endoscope enables the surgeon to operate on tumors located in the suprasellar region under direct visualization. When the adoption of endoscopy in transsphenoidal pituitary surgery had demonstrated obvious advantages over conventional microscopic surgery, the use of this endoscopic endonasal technique has been expanded to include other skull base lesions at the anterior fossa skull base, cavernous sinus, clivus and clival posterior fossa. In this chapter, the author describes the evolution of this endoscopic transsphenoidal surgery, the pertinent sinonasal anatomy related to transsphenoidal endoscopy, the details of endoscopic endonasal transsphenoidal pituitary surgery, surgical approaches to the other skull base lesions, surgical results, and potential complications and their avoidance.