Thermal injury is the primary mechanism of lesion formation during radiofrequency catheter ablation procedures. Irreversible tissue injury requires heating to approximately 50 degrees C. Temperatures above 100 degrees C result in coagulum formation. Because of this importance of temperature during radiofrequency catheter ablation procedures, temperature monitoring has been proposed as a tool to facilitate catheter ablation procedures. The results of recent clinical studies demonstrate that electrode temperatures do not differ at successful and failed ablation sites, electrode temperature does not predict or eliminate the possibility of arrhythmia recurrence, and closed-loop temperature control decreases but does not eliminate the development of coagulum nor guarantees that target temperatures will be achieved. These observations are due in large part to the important distinctions between electrode temperature, the temperature at the electrode-tissue interface, and the temperature at the ablation target. Nonetheless, temperature monitoring and temperature control are valuable tools during radiofrequency ablation procedures as they provide important information regarding the adequacy of tissue heating, minimize the development of coagulum, and maximize lesion size.