The magnetic fields generated by electrical currents in the human body, such as in the brain and in the heart, can be measured using Super Conducting Quantum Interference Devices (SQUID). We present two methods by which these magnetic field measurements can be processed to obtain images of the electrical current distributions which caused them. These two methods are: reconstruction using Fourier transform techniques and reconstruction using linear estimation theory. We present a brief overview for both methods including computer-simulated reconstructions of biological activity.