This paper describes the posterior segment of eye, the pathology of various retina) diseases (e.g. age-related macular degeneration, diabetic macular edema, and diabetic retinopathy) and various novel drug delivery systems designed for treatment of the diseases. The eye is primarily divided into anterior and posterior segments. Both segments are protected by anatomical and physiological barriers, including specific tissue barriers as well as blood-aqueous and blood-retina barriers. The blood-aqueous barrier consists of the epithelial (non-pigmented ciliary epithelium layer, posterior iridial epithelium, iridial vessel) and the endothelium. This barrier maintains the composition of aqueous humor. The blood retina barrier operates at two levels: inner blood retina barrier (the endorhelial membrane of retina! vessel) and outer blood retina barrier (or chorioepithelial interface or retina! pigment epithelium). The blood retina barrier restricts inward movement following periocular or systemic drug administration and outward movement after intravitreal administration. The route of drug administration is dependent on the site in the eye where the drug is needed. Ophthalmic drugs can be delivered by topical ocular administration (for delivering the drug to an terior segment tissues), systemic administration ( usually associated with the systemic side effects), periocular (subconjunctival, retrobulbar, peribulbar and sub-tenon) or intraocular (usually intravitreal) administration. Periocular or intraocular administration are used for delivery to posterior segment tissues such as the retina. Advances in the ocular nanoparticulate drug delivery systems (e.g. nanoparticles, micelles, dendrimers, liposomes) are expected to provide new tools for the treatment of the eye diseases. Liposome technology has been used to develop light-induced systems for the retina! diseases (Visudyne). The gene based drugs have been used in the treatment of ocular diseases. For instance, fomivirsen sodium (Vitravene) is in the clinical use for the treatment of CMV infection in the AIDS patients. Furthermore, pegaptanib sodi um (Macugen) is an anti-VEGF aptamer for the treatment of wet age-related macular degeneration. The ocular implants are classified as non-biodegradable and biodegradable devices. Non-biodegradable implants can provide more accurate control of drug release and longer release periods in comparison with biodegradable implants. Non-biodegradable systems require surgical implant removal with the associated risks. Vitrasert (ganciclovir delivery device) and Retisert (fluocinolone acetonide delivery device) are clinically used non-biodegradable implants.