This open-access book presents recent advances in our understanding of the nano-structure of synaptic junctions in terms of their organization, mechanisms of assembly, and role in neuronal signaling as well as plasticity. Traditionally, a single synapse was assumed to have a homogeneous organization of molecular components both at the active zone and postsynaptically. Recent advances in imaging tools and the further elucidation of the physiological significance of distinct forms of release have challenged this notion. This is a timely book that will richly contribute to the ongoing efforts to develop this novel perspective into the study of the nervous system.