This course will discuss the nature of Eustachian tube dysfunction (ETD), pathophysiology and medical/surgical treatment with a focus on the most common problem, obstructive ETD. There is increasing evidence that the middle ear and mastoid space is physiologically analogous to an accessory sinus, which shares similar respiratory mucosa and pathology with the nasal cavity and paranasal sinuses. The special sensory functions of the ear are optimized and protected by the Eustachian tube, which serves as a unique, long, curved, and dynamic "ostium." The cartilaginous portion contains a functional valve that must open periodically to allow for ventilation and clearance of secretions. It must close competently to prevent reflux of material and sounds from the nasopharynx. Failure of one or more of these three functions, ventilation, clearance, and prevention of reflux, constitutes Eustachian tube dysfunction (ETD), which represent a spectrum from obstructive to patulous dysfunction. The most common etiology of obstructive ETD is inflammation within the cartilaginous portion causing a functional obstruction. The initial management of obstructive ETD should be to try to identify its source and treat the inflammation appropriately if possible. The course will emphasize endoscopic identification of pathology and targeted surgical treatment. It will build on the AAO-HNS Clinical Consensus Statement on balloon dilation of the Eustachian tube.