Olfaction is an essential chemosensory system in the living world. Although less appreciated in humans, smell impairment significantly affects many aspects of quality of life. Smell disorders may be caused by an impaired nasal airway or by lesions in the olfactory system, leading to reduced or distorted smell perception. The most common causes of smell disorders are aging, upper respiratory tract infection, sinonasal disease, and head trauma. Recovery is rarely complete. Counseling is important in progressive or severe smell loss. In patients with distorted smell perception, antidepressant medication is sometimes necessary. Best response to treatment is achieved for nasal obstruction and sinonasal inflammatory disease. Treatment of olfactory impairment caused by sinonasal disease includes medication with topical and systemic steroids, or surgery for refractory cases. Although there are reports that surgical resection of olfactory neurons may lead to reinnervation and recovery of smell, adequate treatment of the smell loss remains an unmet need.