Alopecia areata (AA) is a common, inflammatory, nonscarring type of hair loss. Significant variations in the clinical presentation of AA have been observed, ranging from small, well-circumscribed patches of hair loss to a complete absence of body and scalp hair. Patients affected by AA encompass all age groups, sexes, and ethnicities, and may experience frustration with the unpredictable nature of their disease for which there is currently no definitive treatment. The cause of AA remains incompletely understood, though it is believed to result-at least in part-from a loss of immune privilege in the hair follicle, autoimmune-mediated hair follicle destruction, and the upregulation of inflammatory pathways. Patients with AA frequently experience marked impairment in psychological well-being, self-esteem, and may be more likely to suffer from psychiatric comorbidities. Part one of this two-part continuing medical education series describes the epidemiology, clinical evaluation, prognosis, and recent advancements in the understanding of the pathogenesis of AA.