Lectins are a large group of proteins found in animals, plants, fungi, and bacteria that recognize specific carbohydrate targets and play an important role in cell recognition and communication, host-pathogen interactions, embryogenesis, and tissue development. Recently, lectins have emerged as important biomedical tools that have been used in the development of immunomodulatory, antipathogenic, and anticancer agents. Several lectins have been shown to have the ability to discriminate between normal cells and tumor cells as a result of their different glycosylation patterns. Furthermore, the specific binding of lectins to cancer cells has been shown to trigger mechanisms that can promote the death of these abnormal cells. Here, we review the importance of lectins-carbohydrates interactions in cancer therapy and diagnosis. We examine the use of lectins in the modification of nanoparticles (liposomes, solid lipid nanoparticles and other polymers) for anticancer drug delivery. The development of drug delivery systems (liposomes, alginate/chitosan microcapsules, alginate beads) carrying some antitumor lectins is also discussed. In these cases, the processes of cell death induced by these antitumor lectins were also showed (if available). In both cases (lectin-conjugated polymers or encapsulated lectins), these new pharmaceutical preparations showed improved intracellular delivery, bioavailability and targetability leading to enhanced therapeutic index and significantly less side effects.