Snake venoms are complex mixtures of biologically active proteins and polypeptides. These toxins belong to a small number of superfamilies of proteins. The members in a single family show remarkable similarities in their primary, secondary and tertiary structures. At times, however, they differ from each other in their biological targeting and hence their pharmacological effects. In other words, each family of protein toxins has a similar molecular scaffold but exhibit multiple functions. Thus structure-function relationships and the mechanisms of action of snake venom proteins are intriguing and pose exciting challenges to scientists. Some of the well-recognized families of venom proteins are: (1) phospholipase A2 (PLA2) family; (2) serine proteinase family; (3) metalloproteinase family; (4) three-finger toxin family; (5) proteinase inhibitor family; and (6) lectin family. We have contributed to the structure-function relationships and mechanism of action of the following families of proteins.