Functional endoscopic sinus surgery (FESS) attempts to restore normal physiologic function of the sinuses via correction of underlying anatomical abnormalities and obstruction. The term functional refers to strategies aimed at preserving the natural drainage pathways of the sinuses. It is important to note that FESS does not cure sinonasal disease but rather facilitates the healing process by improving sinus ventilation and drainage allowing for gradual resolution of mucosal disease. Post-surgical changes also facilitate the delivery of saline and intranasal steroid medications to the paranasal sinus cavities. In this episode, we will discuss the relevant anatomy, pathophysiology, clinical presentation and treatment of chronic rhinosinusitis (CRS) with a specific emphasis on functional endoscopic sinus surgery (FESS) Learning Objectives Describe the anatomy and function of the paranasal sinuses Define functional endoscopic sinus surgery (FESS) Define chronic rhinosinusitis (CRS) List the complications of functional endoscopic sinus surgery (FESS)