Medicinal chemists play a key role in drug design. They are expected to synthesize, purify and analyse novel bio-active compounds. Such organic leads once identified, are easy to exploit. This process is rather straight forward. The real test resides with the identification of such 'lead' compounds and the optimum bioactive positions on the basic skeleton of such leads. The intention of the authors is to provide, within a manageable compass, a general background information to cater to the needs of the students of medicine, pharmacy and science.