Abstract The diversity of air-breathing fishes is reflected in the range of organs they use for aerial respiration, which include the lung, the gas bladder, the buccal, branchial, and opercular chambers, the esophagus, pneumatic duct, stomach and intestine, the gills, and skin. These organs are collectively termed air-breathing organs (ABOs). Lungs are the functional ABO in two primitive groups, the lungfish and the polypterids; all other primitive air breathers use a respiratory gas bladder. Although these two organs are homologous and it is thought that the gas bladder evolved from the lung, the steps in this transition remain problematic. In addition, respiratory gas bladders appear to have independently evolved in many derived teleosts. The other types of ABOs reflect the evolutionary course of teleosts in which the gas bladder became lost or so specialized that its morphology was beyond the point remodeling for aerial respiration. The respiratory epithelium in fish ABOs ranges from complex to simple. Many amphibious fishes breathe air using little more than gills and skin, which in some cases have specializations for amphibious breathing. Air-breathing ventilation entails gulping, buccal force pumping, swallowing, organ contraction, coughing, emesis, and flatulence. In anabantoids and channids, which have noncompliant ABOs, hydraulic pumping and normal and reversed flows similar to coughing are used to replace old air with new air.