Summary Perineuronal nets (PNNs) are meshed‐like extracellular matrix structures present on the surface of sub‐populations of neurons and are involved in regulating plasticity in the central nervous system (CNS). PNNs are formed at the end of the critical period during development and their formation closes the critical period for plasticity, as demonstrated in ocular dominance plasticity. One of the major components of PNNs are chondroitin sulphate proteoglycans (CSPGs), a family of inhibitory molecules for neuronal growth and regeneration. CSPGs are highly up‐regulated after injury in the CNS, including spinal cord and optic nerve. Enzymatic removal of CSPGs in the PNNs enhances plasticity, allows re‐organisation of circuitry and improves functional recovery. Recently, we also observed specific changes in chondroitin sulphate composition in ageing brains when compared to young adult brains. This change may underlie the loss of plasticity in ageing animals. We shall discuss the role of PNNs in regulating plasticity, regeneration and rehabilitation in the CNS, including the visual system in this talk.