Topical administration of drops is by far the most common and convenient way to administer drug to the eye.However, the efficiency of this route of delivery remains poor.Much of the failure of topical drug delivery is caused by poor compliance and difficulties with administration; however very low bioavailability also limits the effectiveness of topical ophthalmic medications.The bioavailability ranges from 1 to 5%.To improve therapeutic efficacy, the ophthalmic formulation scientist must take into consideration the unique anatomy and physiol. of the eye.This chapter will review the ocular surface anatomy and physiol. and discuss their impact on ophthalmic product development.The structure and function of the tear film, eyelids, and nasolacrimal system will be overviewed.Further, the impact that conjunctival and corneal permeability and absorption have on bioavailability will be discussed.The goal of this chapter is to provide an overview of the ocular surface anatomy and physiol. relevant to drug delivery to enable engineering of optimized ophthalmic delivery systems.