Lectins are involved in a range of biological mechanisms related to recognition and binding to carbohydrates. This ability is possible due to the presence of a carbohydrate recognition domain with capacity to differentiate between various oligosaccharides without modify the molecules which it binds. The study of lectins, inserted in the field of Glycobiology, started with Stillmark’s work with castor bean extract and continues until today with the use of advanced techniques such as robust hemagglutination assay and affinity chromatography. Lectins are particularly abundant in plants where seem to be involved in seed maturation or dormancy, plant defense, storage material, and N2 fixation. Furthermore, lectin plants show immunomodulatory effects through signal-transduction system and consequent cytokines production, a research field founded by Ehrlich and his studies with mice immunization. Here we focus on plant lectins and their role in plant physiology, immune response, and structural analysis.