The brain is responsive to an ever-changing environment, enabling the organism to learn and change behaviour accordingly. Efforts to understand the underpinnings of this plasticity have almost exclusively focussed on the functional and underlying structural changes that neurons undergo at neurochemical synapses. What has received comparatively little attention is the involvement of activity-dependent myelination in such plasticity and the functional output of circuits controlling behaviour. The traditionally held view of myelin as a passive insulator of axons is changing to one of lifelong changes in myelin, modulated by neuronal activity and experience. Here we review the nascent evidence of the functional role of myelin plasticity in strengthening circuit functions that underlie learning and behaviour