Galectins (Gal) are proteins that bind to carbohydrates in a non-enzymatic manner and have high specificity for their sugar groups, especially βgalactosides. This protein family includes 15 members (galectins 1-15), of which 12 genes have been identified in humans. At the cellular level, the role and importance of Gal is based on mediating adhesion and binding of molecules to target cells and participation in signaling pathways within the cell, as well as modulation of functions and tasks within the organism. Numerous scientific studies have shown that Gal is mainly expressed in the cells of the immune system, where it plays an important role in the development and progression of infectious and especially non-infectious diseases, particularly oncological diseases. To date, a correlation has been demonstrated between the expression of Gal-1, Gal-2, Gal-3, Gal-4, Gal-7, and Gal-8 and the development of certain cancers, where increased expression has been detected, and thus these proteins can be considered as specific indicators of certain cancers and subtypes. In addition, studies demonstrating expression or suppression of a specific Gal during progression have shown the property of invasiveness and further growth. Therefore, the resulting changes in Gal expression are expected to provide a new approach to the therapy of certain cancers and subtypes, i.e., they will enable new therapies with greater efficacy than those currently available. Given the role of Gal in the immune response, a new therapeutic approach will also be possible for other non-infectious diseases.