The retina is a sensory structure of the central nervous system that initiates the perception of vision. Due to its highly organized and laminar structure, and its well-defined connectivity patterns, the retina provides an ideal model to elucidate the mechanisms of neural circuit formation. Additionally, study of the mouse retina across genetically dissimilar strains facilitates the identification of genes necessary for its development. In this dissertation, three features of neural circuits will be examined in the mouse retina in order to determine the mechanisms underlying their establishment. First, the genetic control of neuronal population size will be determined for three retinal neurons that participate in the same microcircuit, and the degree to which they are co-regulated will be assessed. Second, the plasticity of neuronal differentiation will be determined for neurons of the outer retina by manipulating the composition of cells in the local environment. Finally, a molecular requirement for the assembly of neural mosaics will be identified for one type of retinal neuron. Through these analyses we will gain insight into how the complexity of nervous system arises, which is relevant for the advancement of genetic and cellular therapies.