In prokaryotic organisms, a substantial fraction of adjacent genes are related functionally and most of these are organized into operons. Operons are a group of co-directionally organized genes in prokaryotic genomes with the presence of a common promoter and terminator. Operons provide insight into the cellular functions and also help in determining distinct experimental designs. It is now clear that the structure of an operon is not static but rather changes with environmental conditions in bacterial species.