For hundreds of years, ground-based observatories, and recently satellites, have been continuously measuring geomagnetic field variations. Using archeological materials and shipboard logs, we can extend these records back many millennia. On the other hand, investigating long-term (>1 Myr) variations, which have been linked to changes in Earth’s deep interior, is more difficult and requires extensive investigation and large quantities of high-quality paleomagnetic data. If these variations can be well-determined, they, coupled with geodynamo simulations, provide a unique tool for investigating the deep Earth through time. Despite the challenges that face long-term magnetic field characterization, through continuous effort by our community via data collection, reliability assessment, large-scale analysis, method development, and numerical simulations, extensive advances have been made. In this session, we invite contributions that help assess these long-term variations, and their potential causes, providing insight into Earth’s paleomagnetic field behavior and the deep interior going back in geologic time.