Clinicians routinely practice in a state of incomplete information--about the patient, and about medical knowledge pertaining to patients' care. Consequently, there is now growing interest in the use of CDSS to bring decision support to the point of care. CDSS can impact physician behavior in routine practice. Nonetheless, CDSSs are meant to support humans who are ultimately responsible for the clinical decisions, rather than replace them. Although the adoption of CDSS has proceeded at a slow pace, there is a widespread recognition that CDSSs are expected to play a crucial role in reducing medical errors and improving the quality and efficacy of health care. This will be facilitated by the gradual maturation of electronic health record systems and the emergence of standard terminologies and messaging standards for the exchange of clinical data.