ABSTRACT: Usually, researchers find the difficulties for the development of novel drug delivery systems by imple-menting the novel technologies. Also there are lots of challenges to make these systems site specific for effective drug delivery for extended period of time. A novel biodegradable, injectable polymeric system namely in-situforming implants (ISFIs) looks very promising drug delivery system.In-situ gel formation of drug delivery systems can be defined as a liquid formulation generating a solid or semisolid depot after administration. It is a blend of drug and biodegradable polymers dissolved or suspended in pharmaceutically acceptable water-miscible organic solvents. These are generally liquid formulations that form semi-solid or solid depots after injection at the injection site due to phase separation and provide a prolonged release over weeks to few months duration.After subcutaneous injection of ISFIthe organic solvent dissipates into the surrounding tissue as water penetrates in, this leads to phase separa-tion and precipitation of the polymer forming a depot (gel) at the injection site. The drug entrapped in the depot is then slowly released out into the surrounding body fluid due to the degradation of the polymers and finally reaches the systemic circulation. These high-value formulations ensure patient compliance; will contribute in the design and development of biotechnologically based products. The present review mainly focuses on advantages, disadvantages, classification, composition, methods and evaluation of in-situgelling implants.