The magnetoencephalographic signal is the magnetic field recorded outside the scalp of the head. It is believed to originate from the combined activity of large populations of neurons. In forward models of MEG signals, the neural output is typically represented in terms of equivalent current dipoles. We here go through the mathematical equations for computing MEG signals from current dipoles, present computer simulations of MEG signals using simplified models of the head geometry, and show how the predicted MEG signals depend on the chosen head model and orientations of the dipoles. We also present a formalism for modeling the magnetic field inside brain tissue.