Calcium/calmodulin-dependent protein kinase II (CaMKII) is thought to be a critical mediator of neuronal plasticity that links transiently triggered Ca(2+) signals to persistent changes in neuronal physiology. In one of its roles, CaMKII is an essential player in the N-methyl-D-aspartate receptor-mediated increase in conductance at glutamatergic synapses, a process described as long-term potentiation, which serves as a common model for neuronal plasticity and memory. Recent studies have used genetic, biochemical, live cell imaging and mathematical modeling approaches to investigate neuronal CaMKII and have led to a model of the molecular steps of CaMKII translocation and activation that can explain its role in neuronal plasticity.