**1. Introduction**

This chapter will review literatures concerning glutathione S-transferases from a broad point of view but with an emphasis on their properties, functions, and purification strategies and its challenges. The focus will be on the occurrence of GSTs in insects and the understanding of their role in insecticide resistance. The intention of this review will also be to look into the relationship of particular isoforms of the GSTs to responses to most used insecticides in agriculture.
