The first descriptions of intermittent laryngeal obstruction associated with dyspnea and noisy breathing were reported by Dunglison1 in 1842, Flint2 in 1868, and Osler3 in 1902. MacKenzie4 initially observed abnormal vocal cord motion in 1869. Since those early times, numerous terms have been used to describe abnormal vocal cord movement in the absence of other medical diseases (Table 1).5-20 In 1983, Christopher et al21 published a comprehensive description of a syndrome of vocal cord adduction with a posterior chink (glottic opening) presenting as asthma with symptoms of dyspnea and noisy breathing. The clinical entity was termed vocal cord dysfunction (VCD) and has been popularized predominantly by pulmonologists, allergists, and respiratory therapists. Another term, paroxysmal vocal fold (cord) motion (PVFM), has been used primarily by otolaryngologists, speech pathologists, and speech therapists to describe the associated endoscopic findings of laryngeal obstruction. Unfortunately, both VCD and PVFM have inadvertently become collective terms for other several clinical presentations due to glottic disorders. We believe that VCD, PVFM, and laryngomalacia (a supraglottic disorder) are better encompassed by the term periodic occurrence of laryngeal obstruction (POLO). This article focuses on VCD and PVFM, the glottic disorders. These entities remain poorly understood and inadequately characterized with regard to etiology, pathophysiology, and management.22 Few prospective series and comprehensive studies have been done, whereas case reports, retrospective evaluations, and review articles dominate the literature. In view of the general lack of distinction between VCD and PVFM in publications, the acronym VCD will be used throughout this article. We carefully examine the available retrospective and prospective evidence to establish the following parameters: (1) causative or associated factors with VCD, (2) differential diagnosis of movement disorders of the upper airway, and (3) clinical, spirometric, and endoscopic criteria for the diagnosis of VCD.