Gut microbiota are known to impact multiple organs including the lung. The cross talk between gut microbes and lungs, termed as the “gut–lung axis,” is vital for immune response and homeostasis in the airways. In this chapter, we summarized the coordinated development of microorganisms in the gut and lung, exogenous and endogenous factors related to the cross talk, the mechanisms of the gut–lung axis and their dysbiosis in lung diseases. Although the current understanding of the gut–lung axis is in its infancy, several gut microbiota-associated strategies have been designed to treat and prevent lung diseases.