Selector-only memory (SOM) has emerged as a promising memory concept for high-density cross-point and three-dimensional vertical X-point (VXP) architectures by integrating selector and storage functions within a nanoscale single active material. In contrast to conventional one-selector-one-resistor (1S1R) cross-point memories, SOM exploits polarity-dependent threshold-voltage (V_th) modulation in amorphous chalcogenide materials, enabling nonvolatile information storage while retaining volatile selector behavior. This review provides a systematic overview of recent advances in SOM. The threshold-switching behavior and microscopic mechanisms of polarity-dependent V_th shift that govern SOM operation are first discussed. Strategies for improving device performance and reliability are then summarized, followed by recent progress in SOM-oriented materials screening and device modeling. Advances in array-level integration and industrial demonstrations are subsequently highlighted. Finally, the key challenges limiting the further development of SOM are discussed, and possible routes toward their resolution are outlined.