U.S. health care costs currently exceed 17% of GDP and continue to rise. One fundamental reason that providers are unable to reverse the trend is that they don't understand what it costs to deliver patient care or how those costs compare with outcomes. To put it bluntly, few health care providers measure the actual costs for treating a given patient with a given medical condition over a full cycle of care, or compare the costs they incur with the outcomes they achieve. What isn't measured cannot be managed or improved, and this is all too true in health care, where poor costing systems mean that effective and efficient providers go unrewarded, and inefficient ones have little incentive to improve. But all this can be remedied by exploring the concept of value in health care and carefully measuring costs. This article describes a new way to analyze costs that uses patients and their conditions--not organizational units or narrow diagnostic treatment groups--as the fundamental unit of analysis for measuring costs and outcomes. The new approach, called time-driven activity-cased costing, is currently being implemented in pilots at the Head and Neck Center at MD Anderson, the Cleft Lip and Palate Program at Children's Hospital in Boston, and units performing knee replacements at Schön Klinik in Germany and Brigham & Women's Hospital in Boston. As providers and payors better understand costs, they will be positioned to achieve a true "bending of the cost curve" from within the system, not in response to top-down mandates. Accurate costing also unlocks a whole cascade of opportunities, such as process improvement, better organization of care, and new reimbursement approaches that will accelerate the pace of innovation and value creation.