ABSTRACTControlled drug delivery technology is concerned with systematic release of pharmaceutical agent to maintaintherapeutic level of drug in body for sustained period of time. Conventional drug delivery system results in undesirableside effects due to fluctuating plasma drug level, high peak-to-trough variations, inability to maintain plasma drugconcentration in therapeutic range, larger doses in order to obtain adequate therapeutic effect may result in undesirable,toxicological and immunological effects in non-target tissues. An appropriately designed controlled release system can bea major step toward solving the problem associated with conventional drug delivery system. This review article includesthe history and basic rationale behind controlled drug delivery system. A variety of approaches have been investigated forcontrolled release of drugs and targeting to selective sites which includes polymeric microspheres, liposomes and solidlipid nanoparticles. Microparticles are characteristically free flowing powders consisting of proteins or synthetic polymershaving a particle size ranging from 1-1000 μm. Microparticles have numerous medical applications such as oral, vaccine,intranasal and ocular delivery of drugs. A detailed focus has been given on preparation techniques of microparticles viz.solvent evaporation method, spray drying method, freeze drying technique, hot pressure homogenization method, thermalcross-linking method and coacervation phase separation method. The range of techniques for preparation of microparticlesoffers a variety of opportunities to control aspects of drug administration and enhance therapeutic efficacy.KEY WORDS: Controlled drug delivery system, conventional drug delivery system, microspheres, liposomes,therapeutic efficacy.