Brain plasticity may be defined as long-term alteration in behavior related activity of distributed neural systems. Functional imaging, and particularly functional MRI, allows to investigate the mechanisms underlying brain plasticity. Two aspects may be distinguished: one is learning in healthy subjects; the other is functional reorganization following or associated with acute or chronic brain injury. Because functional MRI is totally non invasive, it appears well suited to follow such reorganization over time. This theme will be developed in the following text.