Myelin plasticity, the capacity for dynamic changes in myelination and myelin structure, challenges the long-held view of myelin as a static entity post-development. Emerging evidence highlights its pivotal role in adapting neural circuits during learning, memory, and recovery from injury or disease. This chapter explores the cellular and molecular mechanisms underlying myelin plasticity, focusing on activity-dependent and experience-driven myelination mediated by oligodendrocytes, which are potentially modified by astrocytes and microglia. This study examines how neuronal activity regulates oligodendrocyte differentiation and myelin remodelling, affecting conduction velocity and circuit synchronization. The implications of myelin plasticity in cognition, ageing, and pathologies such as multiple sclerosis and stroke are discussed alongside experimental models that elucidate its processes. Finally, the importance of sleep in myelin maintenance and plasticity is discussed. Elucidating the mechanisms underlying myelin plasticity and maintenance may uncover new therapeutic opportunities for treating diseases and injuries that disrupt myelin and neuronal activity.