Many forms of synaptic plasticity require NMDA-type glutamate receptors (NMDAR). These tetrameric receptors consist of two obligatory NR1 subunits and two regulatory subunits, usually a combination of NR2A and NR2B. In the neonatal visual cortex NR2B-containing NMDAR predominate, after thatvisual experience facilitates a developmental switch in which NR2A levels increase relative to NR2B. In this review, it puts emphasis on the role and the regulation of this shift as well as the effect on synaptic plasticity.