Preface to <i>Excerpts From the 2025 ESAC Conference on X‐Ray Quasi‐Periodic Eruptions and Repeating Nuclear Transients</i>

ABSTRACT A series of extreme‐variability phenomena associated with supermassive black holes (SMBHs) in galactic nuclei are being revealed with increasing frequency in recent years thanks to enhanced survey capabilities across the electromagnetic spectrum. The observation of these extreme phenomena has opened the way to the study of the physics of SMBHs in real time—something that, until a decade ago, was exclusively associated with stellar‐mass black holes. A conference to discuss the physical processes powering these objects was held at ESAC, Madrid, Spain in June 2025.