This chapter gives an overview of the human visual system. We start from eye optics, which direct light to the retina, where the optical-to-electrical signal transduction takes place. We describe a few basic facts about the retina, focusing on the structure and functions of retinal processing. We then briefly talk about processing that takes place after the retina, i.e., in the Lateral Geniculate Nucleus (LGN) and in the visual cortex.