Gephyrin is a multifunctional protein responsible for molybdenum cofactor synthesis and the clustering of glycine and GABA_A receptors at inhibitory synapses. Based on the structure of its two conserved domains, G and E, gephyrin is thought to form a hexagonal lattice serving as a scaffold for accessory proteins at postsynaptic sites. However, important aspects of gephyrin gene expression, protein structure and regulation, as well as the role of gephyrin in synapse formation and plasticity, remain poorly understood. Here we review the current state of knowledge about gephyrin, highlighting new research avenues based on a different structural model and a revised nomenclature for gephyrin splice variants. Unraveling the biology of gephyrin will further our understanding of glycinergic and GABAergic synapses in health and disease.