There is wide agreement that patients who are informed, active participants in their own care have better outcomes, and their health care is apt to cost less. This article describes the development of the Patient Activation Measure (PAM), the first instrument for measuring the skills, knowledge, beliefs and behaviors that combine to create an activated patient. The authors field-tested their questionnaire by conducting a telephone survey of a national probability sample of 1,515 individuals. They conclude that PAM is valid and highly reliable. It indicates that patients progress through four stages as they become activated. (1) They come to believe their role in their own care is important. (2) They learn enough and develop enough confidence to act on their own behalf. (3) They actually act. (4) They reach the point where they can act even under stress. The researchers note that, by using PAM to identify a patient's stage of activation, physicians can individualize their care plans. PAM can also be used to assess how well such interventions work. The authors state that their instrument will eventually need further refinement.