Neuroligin 3 (NLGN3) is a transmembrane protein that plays an important role in synaptic development. It is expressed during development on astrocytes and Schwann cells as well as on neurons where it localizes to synaptic membranes and post-synaptic densities of both glutamatergic and GABAergic synapses. It associates in cis with Neuroligin 1 and Neuroligin 2 and trans-synaptically with Neurexin-1, -2, and -3 beta that lack the splice site 4 insertion. A soluble form of the Neuroligin 3 ECD can be released by neurons and promotes glioma cell proliferation. Mutations in Neuroligin 3 enhance neuronal dendritic branching, alter both excitatory and inhibitory synaptic activity, and are associated with the development of autism spectrum disorder.