Aggrecan is well-studied in cartilage but its expression and function in the central nervous system has only recently begun to be appreciated. Aggrecan plays an important role in the organization of the neural extracellular space by binding and organizing hyaluronan to the cell surface through interactions with link protein and tenascins forming a large aggregated quaternary complex. While all members of the lectican family to which aggrecan belongs are thought to mediate similar roles in organizing the neural matrix, aggrecan is unique in that it is the only family member found almost exclusively in an enigmatic matrix substructure called the perineuronal net. Current work has established a critical role for perineuronal nets and aggrecan in regulating developmental neural plasticity and in the recover from injury. In this review we focus on the structure, expression and function of aggrecan in the central nervous system.