To predict when earthquakes are likely to occur, seismologists often use statistics to monitor how clusters of seismic activity evolve over time. However, this approach often fails to anticipate the time and magnitude of large-scale earthquakes, leading to dangerous oversights in current early-warning systems. For decades, studies outside the seismology field have proposed that these major, potentially devastating seismic events are connected to a range of non-seismic phenomena—which can be observed days or even weeks before these large earthquakes occur. So far, however, this idea hasn't caught on in the wider scientific community. In this special issue, EPJ Special Topics proposes the Global Earthquake Forecasting System (GEFS): the first collaborative initiative between multi-disciplinary researchers devoted to studying a diverse array of non-seismic earthquake precursors.