Ophthalmic drug delivery is one of the most interesting and challenging endeavors facing the pharmaceutical scientists, the major problem encountered to pharmaceutical scientist is rapid precorneal elimination of the drug, resulting in poor bioavailability and therapeutic response, because of high tear fluid turnover and dynamics. This interest has been sparked by the advantages shown by in situ forming polymeric delivery systems such as ease of administration and reduced frequency of administration, improved patient compliance and comfort. The formation of gels depends on factors like temperature modulation, pH change, presence of ions and ultra violet irradiation, from which the drug gets released in a sustained and controlled manner In situ-forming gels are liquid upon instillation and undergo phase transition in the ocular cul de-sac to form visco-elastic gel and these gels provides a response to environmental changes. In the past few years, an impressive number of novel temperature, pH, and ion induced in situ-forming systems have been reported for sustained ophthalmic drug delivery. Each system has its own advantages and drawbacks. The choice of a particular gel depends on its intrinsic properties and envisaged therapeutic use. Now a days in situ gel have been used as vehicles for the delivery of drugs for both local treatment and systemic effects. In this review basic about in situ gel system covered. From a manufacturing point of view, the production of such devices is less complex and thus lowers the investment and manufacturing cost.