Interest in informed decision making (IDM) has grown in recent years. Greater patient involvement in decision making is consistent with recommendations to improve health care quality. This report provides an overview of IDM; clarifies the differences between IDM, shared decision making (SDM), and informed consent; and reviews the evidence to date about IDM for cancer screening. The authors also make recommendations for research. We define IDM as occurring when an individual understands the disease or condition being addressed and comprehends what the clinical service involves, including its benefits, risks, limitations, alternatives, and uncertainties; has considered his or her preferences and makes a decision consistent with them; and believes he or she has participated in decision making at the level desired. IDM interventions are used to facilitate informed decisions. The authors reviewed the evidence to date for IDM and cancer screening based primarily on published meta-analyses and a recent report for the Centers for Disease Control and Prevention's Guide to Community Preventive Services. IDM and SDM interventions, such as decision aids, result in improved knowledge, beliefs, risk perceptions, and combinations of these. Little or no evidence exists, however, regarding whether these interventions result in 1) participation in decision making at a level consistent with patient preferences or 2) effects on patient satisfaction with the decision-making process. These variables generally either were not assessed or were not reported in the articles reviewed. Results of interventions on uptake of screening were variable. After exposure to IDM/SDM interventions, most studies showed small decreases in prostate cancer screening, whereas four studies on breast and colorectal cancer screening showed small increases. Few data are available by which to evaluate current practices in cancer screening IDM. Patient participation in IDM should be facilitated for those who prefer it. More research is needed to assess the benefits of IDM/SDM interventions and to tailor interventions to individuals who are most likely to desire and benefit from them. There are many system barriers to IDM/SDM and few tools. More work is needed in this area as well. In addition, research is needed to learn how to incorporate IDM into ongoing clinical practice and to determine whether there are unintended negative consequences of IDM.