Despite extensive research in the field, the major problem in ocular drug delivery is the attainment of an optimal drug concentration at the intended site of action for a sufficient period of time. The site of action maybe located on the eye surface or in the inner ocular structures. The important barriers that need to be overcome in order to reach the target site limits not only the number of medications available for the treatment of ocular diseases, but aIso the extent to which those available can be used without incurring undesirable systemic side effects. From the results described in this chapter, it is possible to conclude that nanoparticles offer great chances of solving these limitations, while still benefiting from their topical administration as eye drops. Indeed, nanoparticles, depending on their composition, are significantly retained on the ocular mucosa, and from this location, they deliver the associated drugs for extended periods of time. This situation normally results in an enhanced and prolonged therapeutic response, and also in a decrease in the side effects. The results reported so far have also evidenced that both the extent of interaction and the penetration depth of the colloidal systems with the cornea, can be modulated by the selection of an appropriate coating. In addition to these beneficial effects associated with the topical ocular administration, nanoparticles offer an interesting potential in terms of improving intraocular drug administration. This potential includes not only the prolongation of the residence time of drugs in the eye, but also their targeting to the retina! cells. Finally, significant efforts are currently underway to develop highly sophisticated nanoparticles functionalized with specific targeting ligands (i.e. lectins and antibodies). Advances in this area are expected to open new avenues for the diagnostic and therapy (including gene therapy) of ocular disorders.