This video explains the basis of M/EEG signals, and instrumentation, with a focus in the differences between both techniques. Firstly, some basic concepts (i.e. both techniques measure post-synaptic potentials). Secondly, instrumentation is detailed: passive/active shielding, how environmental noise is supressed with an axial gradiometer,etc. Finally, EEG and MEG are compared in detail (i.e. which currents are visible in MEG but not in EEG, or vv.).