Efforts to improve the quality and value of health care increasingly emphasize a critical role for the meaningful use of clinical decision support systems (CDSSs) and electronic knowledge management systems (KMSs). For the purpose of this review, a clinical decision support system is defined as "any electronic system designed to aid directly in clinical decisionmaking, in which characteristics of individual patients are used to generate patient-specific assessments or recommendations that are then presented to clinicians for consideration." Examples of electronic CDSSs include alerts, reminders, order sets, drug-dosage calculations, and care-summary dashboards that provide performance feedback on quality indicators or benchmarks. In contrast, a knowledge management system is defined as a tool that selectively provides information relevant to the characteristics or circumstances of a clinical situation but which requires human interpretation for direct application to a specific patient. Examples of electronic KMSs include information retrieval tools and knowledge resources that consist of distilled primary literature on evidence-based practices. An information retrieval tool is defined as an electronic tool designed to aid clinicians in the search and retrieval of context-specific knowledge from information sources based on patient-specific information from a clinical information system to facilitate decisionmaking at the point of care of for a specific care situation. A knowledge resource is defined as an electronic resource comprising distilled primary literature that allows selection of content that is germane to a specific patient to facilitate decisionmaking at the point of care or for a specific care situation. The objective of a CDSS is to apply clinical knowledge in the context of patient-specific information to aid clinicians in the process of making decisions. Electronic KMSs can further support decisionmaking in any care situation by providing a range of strategies and resources to create, represent, and distribute knowledge for application by a human in clinical practice. As a form of health information technology, CDSSs and KMSs can serve as information tools to align clinician decisionmaking with best practice guidelines and evidence-based medical knowledge at the point of care as well as assist with information management to support clinicians' decisionmaking abilities. This evidence report is part of a three-report series focusing on the strategic goals of the Agency for Healthcare Research and Quality's (AHRQ's) health information technology portfolio. This report specifically explores facilitating health care decisionmaking through health information technology. Supporting health care decisionmaking is a core element of the meaningful use criteria for EHRs. As the expected level of sophistication of EHRs increases in the evolving definitions of meaningful use, the need for more sophisticated CDSSs/KMSs is imperative, as is the need for better operational use of these systems. This increasing importance of CDSSs/KMSs acknowledges that EHRs alone are not an end but are instead a tool to augment the delivery of safe, evidence-based, high-quality health care through more consistent and sound decisionmaking. The goals of this report were to summarize the available evidence related to CDSSs and KMSs, highlight the limitations of the evidence, and identify areas for future research. The key questions considered in this review were: KQ 1: What evidence-based study designs have been used to determine the clinical effectiveness of electronic knowledge management and CDSSs? KQ 2: What contextual factors/features influence the effectiveness or success of electronic knowledge management and CDSSs? KQ 3: What is the impact of introducing electronic knowledge management and CDSSs? KQ 4: What generalizable knowledge can be integrated into electronic knowledge management and CDSSs to improve health care quality?