Spontaneous pneumothorax, which may have an acute or insidious onset in dogs and cats, results in respira-tory difficulty and has the potential to be life threatening.1-3 Dogs commonly develop spontaneous pneumo-thorax due to bullae or blebs, while cats typically have underlying inflammatory disease, like feline allergic airway disease. Urgent therapeutic intervention is essential in animals with respiratory distress. The recom-mended therapeutic strategies are typically different in each of these species due to underlying etiology. The first part of this review article will focus on physiology, clinical presentation, and diagnosis of spontaneous pneumothorax in dogs and cats. Advances in diagnostics, especially the recent utility of point of care ultra -sound, will be discussed. The second part of the series will provide an overview of therapeutic options and management of patients with spontaneous pneumothorax, as well as information on prognosis. (C) 2021 The Author(s). Published by Elsevier Inc.