Central neuronal synapses are composed of pre- and postsynaptic compartments that undergo activity-dependent changes required for learning, memory and cognition. Synapses are developed, differentiated and maintained by a class of adhesion molecules known as synapse organizers. Prominent among them are postsynaptic Leucine-rich-repeat transmembrane neuronal proteins (LRRTMs) which mediate robust synaptogenic activity through binding to their presynaptic partners, neurexins. LRRTMs are largely expressed in excitatory synapses and are expressed in discrete patterns throughout the brain. In the hippocampus, they have lamina specific expression in the CA1 and dentate gyrus. The LRRTMs also contribute to AMPA receptor (AMPAR)-mediated transmission and long-term potentiation (LTP). Given the role of LRRTMs in synapse development and their implications in neuropsychiatric disorders such as schizophrenia and autism spectrum disorders (ASD), the lamina-specific expression of LRRTMs within the hippocampus is likely functionally important. This thesis explores the contributions of LRRTMs (LRRTM1-4) in the hippocampus and aims to understand their role in synapse development, plasticity, and cognition. Here, I show that all four LRRTM family members require the heparan sulfate glycan modification of neurexins but use different neurexin protein domains to induce presynaptic differentiation. Our results also indicate that a novel isoform of neurexins, neurexin1-gamma acts as a presynaptic partner of LRRTM3 and LRRTM4. Additionally, this thesis shows that two major presynaptic hubs, neurexins and receptor protein tyrosine phosphatases (RPTPs) interact and contribute to LRRTM4-mediated synaptogenesis. This thesis also addresses the contributions of LRRTM1 and LRRTM2 to developmental stage-specific and context-specific roles in the dorsal hippocampus. LRRTM1 and LRRTM2 also regulate synaptic plasticity and hippocampus-dependent long-term contextual memory in both the developing and mature brain. In conclusion, the thesis has identified several novel molecular mechanisms by which LRRTMs mediate synapse development and plasticity through their interaction with neurexins. These results have broad implications on our understanding of neuropsychiatric disorders and are likely to represent the general theme of context-dependent synaptic specificity in the vertebrate nervous system.