This chapter reviews some of the connections to the motor cortex that have been studied in humans using the technique of transcranial magnetic stimulation (TMS). In all cases a double pulse design has been used in which one stimulus is used to evaluate the excitability of the motor cortex at different times, after another stimulus has been given over a different site in order to activate connections between the two areas. Interhemispheric, cortico-cortical and cerebello-cortical effects are described. The first two have been shown to be task-sensitive and specifically affected in patients with neurological diseases such as epilepsy and movement disorders. © 2002, Elsevier Science B.V. All rights reserved.