A spa is defined as a bathing establishment which used thermal-mineral spring water for therapeutic purposes. Although the topics of bathing and medicine in the Roman world have received considerable attention, thermal-mineral spas have remained inadequately studied. Recent research acknowledges the importance of spas, but generally excludes any detailed discussion of the institution. More than thirty spas are known to have existed in Italy alone together with over a hundred more throughout the Roman provinces. Knowledge of many of these is preserved only in the literary record. Further information about other sites has also been brought to light through inscriptions and archaeological investigation. By using a wide range of evidence, including ancient literary sources, inscriptions, and archaeological material, I have provided a clarification of the nature of Roman healing spas in their original context.