Lung-on-a-Chip (LoC) is a microfluidic device that simulates the gas-liquid interface of the human pulmonary alveoli and is intended for pathophysiological, pharmacological and molecular biological studies of the blood-air barrier in vitro. The LoC device includes a system of liquid and gas microchannels separated by a semipermeable elastic membrane containing a polymer base and cellular elements of the alveoli. Depending on the type of LoC (single-channel, two-channel and three-channel), the membrane may contain only alveolocytes, or alveolocytes in combination with other cells: endothelial cells, fibroblasts, alveolar macrophages, tumor cells, etc. Some LoC models also include a hydrogel stroma that simulates pulmonary interstitium. The first two-channel LoC, in which there is a monolayer of alveolar cells on one side of the membrane and a monolayer of endothelial cells on the other, was developed in 2010 by the group of Ingber et al. at the Wyss Institute of Harvard University in order to reproduce the microenvironment and biomechanics of the alveoli in vitro. Modern modifications of LoC include the same elements and differ only in the design of the microfluidic system, the membrane biomaterial, the composition of the cellular and stromal elements and the special tasks being solved. In addition to LoC that reproduce the blood-air barrier, there are modifications for studying specific pathophysiological processes, screening drugs, modeling particular diseases, such as lung cancer, COPD or asthma. In this review, we analyzed the existing varieties of LoC, the biomaterials used, the methods for detecting molecular processes in microfluidic devices and the main areas of research using the "Lung-on-a-chip" technology.