Repeating earthquakes, or repeaters, are identical in location and geometry but occur at different times. They appear to represent recurring seismic energy release from distinct structures such as slip on a fault patch. Repeaters are most commonly found on creeping plate boundary faults, where seismic patches are loaded by surrounding slow slip, and they can be used to track fault creep at depth. Their hosting environments also include volcanoes, subducted slabs, mining-induced fault structures, glaciers, and landslides. While true repeaters should have identical seismic waveforms, small differences in their seismograms can be used to examine subtle changes in source properties or in material properties of the rocks through which the waves propagate. Source studies have documented the presence of smaller slip patches within the rupture areas of larger repeaters, illuminated earthquake triggering mechanisms, and revealed systematic changes in rupture characteristics as a function of loading rate. ▪ Repeating earthquakes are observed in diverse tectonic and nontectonic settings. ▪ Their occurrence patterns provide quantitative information about fault creep, earthquake cycle dynamics, triggering, and predictability. ▪ Their seismic waveform characteristics provide important insights on earthquake source variability and temporal Earth structure changes.