Regulation of functional AMPA receptor (AMPARs) and NMDAR numbers at post-synaptic sites is a core mechanism for plasticity of excitatory synaptic transmission. AMPAR and NMDAR to a less extent can traffic in and out of synapses by lateral diffusion in the plane of the neuronal membrane. Understanding the processes that regulate AMPAR and NMDAR surface trafficking will likely shed new light on the mechanisms that control receptor concentration at synapses. In this lecture, I will present several lines of evidences showing that the AMPAR and NMDAR surface diffusion is dependent on the subunit composition, the scaffold protein, the neuronal activity status, and the synaptic transmission.