Among sensory abilities, smell and taste are the mechanisms through which humans sample chemicals in the environment, also known as chemoreception. These chemosensory abilities allow us to appreciate pleasurable environmental stimuli and provide critical information for the avoidance of potentially toxic compounds or environmental dangers. Correspondingly, dysfunction of these sensory abilities has repercussions not only for quality of life, but also personal safety. In this module, we will undertake an in-depth discussion of chemosensory dysfunction beginning with definitions of olfactory dysfunction and taste disturbance and associated epidemiology. Normal physiology and pathophysiology of chemosensory disorders are reviewed, along with associations of chemosensory disorders to other diseases of the head and neck. An overview of appropriate components of patient history and physical examination follows, with a discussion of indications for further testing. Finally, treatment modalities and patient outcomes for olfactory dysfunction and taste disturbance are highlighted. This review contains 3 figures, 8 tables and 76 references. Key Words: Olfactory Dysfunction, Gustatory Dysfunction, Chemosensation, Evaluation of smell loss, Evaluation of taste loss, Olfactory Training