Magnetoencephalography (MEG) is a powerful tool for measurement of brain function. Used both in research and clinical investigation, MEG measures magnetic fields generated by current flow through neuronal assemblies. Mathematical modelling of these fields enables generation of 3D images showing moment to moment changes in brain current. In this way, MEG offers a powerful metric, able to track the formation and dissolution of brain networks as they modulate in support of cognition. However, the current generation of MEG scanners are severely limited. This is because the only sensors able to detect the small magnetic fields generated by the brain are superconducting quantum interference devices (SQUIDs) which must be cryogenically cooled to maintain operation. This need for cooling makes MEG systems large and expensive. Moreover, they cannot adapt to head shape or size, they are very sensitive to subject motion, they are largely unsuited to imaging infants and even in adults, the requisite thermally insulating gap between the head and the field sensors limits both sensitivity and spatial resolution.In this talk, I will describe our recent work on the use if a new generation of magnetic field sensor – the optically pumped magnetometer (OPM). OPMs offer similar sensitivity to SQUIDs but without requirement for cryogenic cooling. This has enabled us to develop a new generation of MEG technology (see Figure 1). I will first discuss the basic operation of an OPM including its origins in fundamental quantum physics. I will then go on to describe the development of OPM-MEG, from single sensor recordings to the current 50-channel whole head system which is in operation at the University of Nottingham. I will discuss the technical challenges that have been solved, and which allow for measurement of brain function in freely moving subjects. I will also discuss the latest applications of this technology, including measurements in infants, virtual reality, motor learning and functional connectivity. I will conclude by speculating on the future of MEG technology and the role that can be played by OPM-MEG.