This article assesses the presumption that consumer choice in health care is based on a rational weighing of alternatives--that information consumers about plan or provider performance, when coupled with information on cost plus service scope and limitation, will lead consumers to select high-quality, low-priced plans or providers. The authors review research on what health care consumers know, what they want to know, and what others think they should know. They also consider how people use information in making decisions and what this implies for what consumers really need to know to make effective decisions. The article concludes that assuming a rational consumer does not account for choice among options in the increasingly complex health care context facing consumers today. Based on this review, the article identifies gaps in the knowledge and sketches out a prospective research agenda in the area of consumer health care decision making.