Over the past twenty years, it has become possible to interfere with human brain functions safely and reversibly. The technique, known as transcranial magnetic stimulation (TMS), has become a mainstay of cognitive neuroscience. Depending on the stimulation parameters, information processing in the brain can be either enhanced or disrupted. In this way, the contribution of different brain areas involved in mental processes can be studied, allowing a functional decomposition of cognitive behaviour both in the temporal and spatial domain. This review shows the most important technical and methodological considerations regarding the use of TMS as a tool for cognitive studies.