The magnetic fields around us encode information about the dynamics of nearby magnetic moments and electrical currents. Some of these currents are due to biological activity such as the beating of a heart or the firing of a neuron. The detection of these currents is the basis for clinical diagnostics like electrocardiography (ECG) and electroencephalography (EEG). In many situations however, current measurements are overly invasive or imprecise, and magnetic measurements are preferred. Unfortunately though, the magnetic signals are significantly more difficult to detect, as the world is a very magnetically noisy place. I will in this talk describe the principles of optically pumped atomic magnetometry, some recent applications in biomagnetism and their limitations.