Plasticity of cortical circuits is maximal during critical periods of postnatal development. Ocular dominance plasticity is a classical model to understand the role of experience in development of the visual cortex. Recent studies are beginning to unravel the synaptic mechanisms underlying this form of plasticity and to elucidate the different plasticity of juvenile and adult animals at mechanistic and molecular level. These investigations indicate that this form of plasticity is regulated by factors located at extracellular and intracellular level. The molecular composition of the extracellular environment in which synaptic plasticity occurs changes during development becoming less permissive for plasticity. In addition, visual experience activates epigenetic mechanisms of regulation of gene transcription that becomes downregulated in adult animals.