Lectins are a wide variety of proteins or glycoproteins that have the ability to bind and recognize carbohydrate molecules. They are found in various types of organisms, from viruses to humans. They also have many functions in the organisms, including immune response and pathogen recognition. In particular, plant lectins play a role in the plant defense system by recognizing specific sugar moieties on the surface of pathogenic organisms such as fungi or bacteria. In addition, their activities contribute to the regulation of plant growth and development as well as to symbiotic interactions with beneficial microorganisms in plants. There is information that plant lectins have protective effects on plants against abiotic stress factors such as drought, salinity, and temperature. Despite these diverse functions of the lectins in plants, their consumption can have toxic effects on animals, including humans. Due to their functional properties, which are antimicrobial, anticancer, immunomodulatory, anti-inflammatory, and antiviral, they have also attracted attention in medicine. All of these properties are revealed by their specific binding to cell surface carbohydrates. They are therefore used as diagnostic tools to detect carbohydrate antigens on the cell surface and as therapeutic tools that bind to cancer cell membranes carrying abnormally glycosylated residues of glycoconjugates. Their ability to bind to specific carbohydrate motifs found in certain cell types, including cancer cells, also makes them a potential candidate for targeted drug delivery. The medical applications of plant lectins are still an active field of research and further studies are needed. In addition, their activity and specificity need to be modified for their medical use or their toxic effects need to be investigated much more thoroughly.