Magnetoencephalography (MEG) is the measurement of the weak magnetic fields generated by neuronal activity in the human brain. By measuring the magnetic field evoked when specific sensory stimuli are presented to a subject, a map of the functional organization of the brain can be deduced with a subcentimetre spatial resolution and a millisecond temporal resolution. As well as a tool for fundamental study of the brain, MEG can also be used in clinical studies and assessment of patients with specific neurological disorders.