Performance management systems are considered a key instrument for steering the performance of public sector organizations. Yet, little empirical insight exists on how public-sector professionals use these systems in practice. We know even less about why they use these systems as they do. For instance, most literature on performance management systems in healthcare reports upcoding and patient selection as perverse and financially driven responses of medical professionals. Still, such unintended responses may well be driven by considerations that are more professional in nature, particularly if the system is considered to be at odds with standards, norms, and values of the medical profession. This book explores and interprets the responses of medical professionals to a Diagnosis-Related Groups (DRG) performance management system used for reimbursement of hospitals and medical professionals in the Netherlands. By analyzing unintended responses from both a managerial and a professional perspective, it adds significantly to the predominantly mono-perspective current literature on performance measurement and public management. Based on a large number of in-depth interviews with medical professionals and managerial stakeholders, the author sheds light on the various types of unintended responses applied by medical professionals, as well as on measures taken by managerial stakeholders to address such responses, conflicting interpretations of unintended responses, and opportunities to reconcile such conflicts. The book thus provides valuable reading for scholars in the fields of public management and administration, and for healthcare policymakers and regulators.