The concept of gut-lung axis came about as a result of numerous studies where mechanisms of cross-talk between the lung and gut microbiota (LM, GM) were analysed. Their results can help better understand immunological mechanisms in homeostasis and pathological changes caused by different immune disorders during COPD and other lung diseases. Recently GM dysbiosis was linked to some gastrointestinal diseases and certain inadequacies of the immune system. In fact, research data indicates that the GM is an important moderator of immune responses, inflammation, and the development of lung diseases, such as pneumonia and COPD. Exposure of the lung to the environment leads to it being colonized by various pathogens, which form its microbiota. The cross-talk between the GM and LM is believed to play a role in certain common lung diseases. The exact way the GM affects lung homeostasis and diseases is yet to be understood. However, it is already clear that the GM plays a crucial role in the development of the immune system and can either provide benefits or cause disease susceptibility in the host. Studying the gut-lung axis can help better understand immunological mechanisms in homeostasis and pathological changes caused by different immune disorders during COPD and other lung diseases. There is great potential in manipulating the GM when developing new successful treatments of lung diseases.