Glial control of critical periods for experience-dependent neuronal plasticity. Schematic of glia–neuron interactions that can influence the timing of critical periods for neuronal plasticity. Astrocyte maturation, and specifically the expression of Cx30, regulates activity of the ECM-degrading enzyme MMP9 via RhoA activation to promote ECM stabilization and interneuron maturation. Astrocytes also enhance dendritic stability by regulating microtubules via neuroligin/neurexin signaling, as well as promote the switch from spike timing-dependent long–term depression to spike timing-dependent long-term potentiation during postnatal development via adenosine signaling. Oligodendrocyte maturation and myelination during adolescence modulate dendritic spine stability, cortical responsiveness to sensory stimuli, and cortical inhibitory synaptic transmission. Microglia regulate PNNs via both deposition and degradation of PNN components, as well as engulf ECM surrounding synapses. Furthermore, there is evidence for astrocyte-to-microglia signaling through IL-33, which influences synaptic ECM engulfment, as well as microglia-to-astrocyte signaling through Wnts during development to influence astrocyte contacts with synapses.