In the last decade, air circulators have been widely used in greenhouses and high tunnels in Japan. The main purpose of air circulation is to provide uniformity in temperature, humidity level, and carbon dioxide concentration in greenhouse air. In addition, empirical knowledge that air circulation prevents hygrophilous diseases increased among growers, together with the inference that air circulation reduces the fuel consumption required for heating. Although the benefits of air circulation remain uncertain, some empirical evidence has been obtained from horticultural and engineering studies in Japan. In this review, the results of these investigations are summarized on the basis of five aspects: performance indicators for circulators, microclimate uniformity, crop yield, suppression of hygrophilous diseases and possible mechanisms. Practical issues regarding the installation of air circulators for greenhouses and high tunnels are also discussed.