Endoscopic Sinus Surgery (ESS) is based on the principles of Messerklinger and Stammberger theory and technique. The successful factors of ESS are precisely preoperative diagnosis, clear endoscopic visual field and delicately operative technique. ESS can be a limited surgery to local diseased sinus or pansinusectomy. The operative field may also be extended to neighboring organs around the sinus. It is not necessary to resect the sinus but just to keep pathway of sinus patent to improve ventilation and drainage. Clear operative field depends on less bleeding, skillful manipulation of endoscope and knowledge of regional anatomy. Satisfactory premedication, complete local anesthesia, less trauma to mucosa are necessary to prevent bleeding. For less trauma to mucosa, the traditional instruments of ESS need to have the function of through-cutting. Newly powered instruments and laser focus on preventing tearing of mucosa. When active bleeding interferes the surgical field, operation needs to be stopped and controls bleeding with epinephrine cotton packing or local cauterization. When the complicated anatomic structure cannot be orientated by CT scan or endoscopic finding needs to stop procedure, we should investigate the surgical anatomy by probe or suction tube to check the angle and depth of organ from the nasal columella or by using C-arm, transillumination, trephination or even Computer Image Navigator System to orientate where we are. The process of ESS is from uncinate process, ethmoid bulla ,basal lamella, posterior ethmoid, sphenoid sinus, then proceeding forward to frontal and maxillary sinus, but Wigand likes reversed process (from posterior to forward). This process may prevent troublesome bleeding. The extension of ESS depends on the preoperative CT scan and operative endoscopic findings. The isolated lesion may be treated directly, not necessarily through ordinary process. It is not allowed to open the healthy sinus abruptly. The opening of ostium of sinus is not ”the wider the better”. The principles of management of nasal septum and middle turbinate emphasize on improving physiological function of sinuses, postoperative care and preventing lateralization, synechia of middle turbinate and obliteration of middle meatus.