The enzyme inhibitors are low molecular weight chemical molecules, which can decrease or totally inhibit the enzyme catalytic activity either irreversibly or reversibly. Reversible competitive inhibitors bind non-covalently to the active site of the enzyme and compete with the substrate. Uncompetitive reversible inhibitors bind exclusively to the enzyme-substrate (ES) complex or to subsequent enzyme forms. Noncompetitive reversible inhibitors bind to both the free enzyme and to the ES complex or subsequent enzyme forms. The impact of enzyme inhibitors in drug discovery has become a fundamental approach to pharmacology at any pharmaceutical industry or drug research center. More than 100 enzyme inhibitors are currently marketed and double than those are under development. Such inhibitors exhibit their specific action in enzyme inhibition inside cells, bacteria, virus, and human body. They can be used for the treatment of various disorders and diseases including asthma and chronic obstructive pulmonary disease, cardiovascular diseases, erectile dysfunction, gastrointestinal disorders, hepatitis B virus infection, hepatitis C virus infection, herpes virus infections, human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) and rheumatoid arthritis and related inflammatory diseases.