Does managed care reduce the costs of medical care while leaving the quality of treatment at least unchanged? What instruments should be employed to prevent risk selection? How can medical decision making be based on more rational criteria? This book consists of three major studies, each addressing a specific question related to the current debate on reforms in the health care sector. Insurers offering managed care contracts have the right to deny coverage for treatment prescribed by an insured's physician. In the US, such practices have provoked a wave of criticism against managed care. The first study shows that monitoring physicians' decisions can generally raise the efficiency of health care provision. However, insurers tend to intervene too much in medical decision making, such that consumer welfare may also decline. If premium payments do not reflect individual risk types, insurers have an incentive to practice risk selection (cream skimming). To prevent this, risk adjustment schemes have been introduced in several countries. The second study takes up the critique against conventional risk adjustment and shows that an inaccurate adjustment scheme may even have detrimental effects on social welfare. The optimal payment scheme in the model framework involves partial cost reimbursement based on the insurer's information.Watchfully waiting involves monitoring a patient's health state over time and deciding whether to undertake a medical intervention, or to continue waiting. The third study contains a formal model of the watchfully waiting process. Optimal decision rules for switching to direct medical intervention are derived. The approach could be applied to a wide range of decision problems in health economics and medicine.