The ocular drug delivery is one of the most challenging & interesting endeavors facingthe pharmaceutical companies in the market.  To circumvent the protective barriers of the eye without causing permanent tissue damage is the challenge to the formulator. Hence to improve the bioavailability of ocular drug considerable amount of research has been focused in developing the controlled drug delivery systems. The main aim of preparing the ocular insert is to increase the bioavailability of ocular drug. The Ocular inserts maintain the concentration of drug within the desired range. The Ideal ophthalmic drug delivery must be able to sustain the release of drug & to remain in the vicinity of front of the eye for the prolong period of time. In this review, we have focused on the Barriers for Ocular drug delivery system, mechanism of action, classification of ocular insert.