A new concept in nanotechnology is that of Solid lipid nanoparticles (SLNs), i.e. lipid nanocrystals in water possessing a solid core into which drugs are incorporated. The SLNs combine the virtues of more traditional drug carriers such as liposomes or polymeric nanoparticles while eliminating some of their disadvantages, e.g. the issues of burst release and long term stability in the case of liposomes as well as the problems of residual solvents and bulk production in the case of polymeric nanoparticles. The use of nanoparticles as drug-carrier system is a very attractive possibility to achieve controlled drug release. A clear advantage of SLNs over polymeric nanoparticles is the fact that the lipid matrix is made from physiological lipids, which decreases the danger of acute and chronic toxicity. There are various types of solid lipid nanoparticles and can be prepared using several methods. The present review covers all the aspects of solid lipid nanoparticles including their history, types, methods of preparations, evaluation parameters, advantages over conventional drug delivery systems and pharmaceutical applications which may be helpful in carrying out extensive research in their regards.