John Rothwell is currently Emeritus Professor of Human Neurophysiology at UCL Queen Square Institute of Neurology and Fellow of the Academy of Medical Sciences. His work has provided the theoretical rationale and methodological developments underpinning the use of transcranial magnetic stimulation (TMS) as a novel therapy in stroke and depression. He has been a primary contributor to our understanding of how TMS interacts with ongoing brain activity, and has devised techniques to probe synaptic connections between brain areas that are now used as biomarkers in neurological disease and movement disorders. He has pioneered methods of repetitive stimulation that modulate synaptic plasticity, the basis of behavioural learning. This provides a unique opportunity to influence activity in human cerebral cortex and has opened up new therapeutic opportunities in neurology and psychiatry.