According to the widely accepted definition by Goldstein, "A Lectin is a carbohydrate binding protein or glycoprotein which agglutinates or precipitates glycoconjugates or both". Broadly, lectins are non-immune origin, non-catalytic carbohydrates binding proteins. Previously the term lectin was confined to potent hemagglutinating plant origin proteins. However, nowadays the term lectin is used in broad sense to denote all types of carbohydrate binding non catalytic proteins. Based on the amino acid sequences of available lectins, it is deduced that the carbohydrate binding property of most lectins resides in a polypeptide sequence, which is termed as Carbohydrate-recognition domain. Generally, lectins are classified in five groups on the basis of their affinity for (i) Glucose/Mannose; (ii) Galactose and N-acetyl-D-galactosamine; (iii) N-acetylglucosamine; (iv) L-fucose, and (v) Sialic acid. Lectins have become the focus of intense interest for biologists and in particular for the research and applications in agriculture and medicine.