Studies examining physicians' clinical decisions have demonstrated considerable variation in decisions and practices and identified numerous challenges to effective, efficient, and accurate decision making. Although use of the decision aids and tools described in this article may help overcome many of these challenges, greater self-awareness of the diagnostic reasoning process and the factors influencing decisions also should help improve clinical decisions and reduce variation, irrespective of the use of these tools. Continued research into the determinants and nature of the diagnostic reasoning process will provide additional insights that can be used to develop and apply improved decision aids and corrective procedures to overcome persistent problems.