The Human Neocortical Neurosolver (HNN) is a new user-friendly software package for circuit level interpretation of human EEG/MEG data. The foundation of HNN is a computational neural model that simulates the electrical activity of the neocortical cells and circuits that generate the primary electrical currents underlying EEG/MEG recordings. HNN is a free open source package that was designed for researchers and clinicians, without computational neural modeling experience, to develop and test hypothesis on the circuit origin of their data.