Lectins are proteins or glycoproteins that appear in various organisms and possess the ability to link with precisely defined sugar structures. They constitute a significant element of biological systems, and their physiological role is connected with the process of glycolization at the level of cells, tissues, and the whole organism. Fungal lectins are isolated from fruiting bodies and also the mycelium of numerous species of macromycetes. The physiological role of fungal lectins covers, among other things, participation in the process of forming fruiting body primordia, the creation of mycelium structures easing the penetration of parasitic fungi into the host organism, as well as the identification of appropriate partners during the early stage of mycorrhization. The biological activity of fungal lectins in relation to organisms or animal or human cells apart from the earliest recognized erythroagglutinational ability manifests itself, for example, in phenomena such as lymphomitogenic activity and immunomodulatory properties, suppression of cell proliferation, and antitumor activity (antiproliferative cytotoxic and apoptosis-inducing activities). Numerous lectins, including fungal lectins due to the high specificity of reversible binding with sugars, are widely used in cytochemical and histochemical methods. Fungal lectins have found application in research in the isolation and structure of cell glycoconjugates, the monitoring of changes occurring on the surface of the membranes of cells at various stages of physiological or pathological development. They can be helpful in embryological, microbiological, and taxonomic research. Fungal lectins have constituted a valuable tool for glycobiological studies in biomedical and cancer research. Several fungal lectins, possessing antitumoral, antiproliferative, and immunomodulatory activities are under clinical trial.