Adult primary sensory cortex is not hard wired, but adapts to sensory experience. The cellular basis for cortical plasticity involves a combination of functional and structural changes in cortical neurons and the connections between them. Functional changes such as synaptic strengthening have been the focus of many investigations. However, structural modifications to the connections between neurons play an important role in cortical plasticity. In this review, the authors focus on structural remodeling that leads to rewiring of cortical circuits. Recent work has identified axonal remodeling, growth of new dendritic spines, and synapse turnover as important structural mechanisms for experience-dependent plasticity in mature cortex. These findings have begun to unravel how rewiring occurs in adult neocortex and offer new insights into the cellular mechanisms for learning and memory.