Evidence-based practice is a movement deriving from medicine to measure the effectiveness or the outcome of practical interventions. This concept has been transferred to social work at a time when the profession is under pressure from «managerialism». Evidence-based social work therefore is suspect, even though there is no doubt that knowledge should be the base of professional social work action. «What works» and other narrow concepts of evidence-based practice seem better suited to managerial demands for «accountability» and to political decision-making in respect of financial problems of welfare states than to professional decision-making. On the other hand accountability and political/financial constraints are a reality social work has to cope with anyway. The leading question asked by this book is whether the change in the environment of social work practice can be used as a stimulus for constructive development and whether evidence-based social work can be conceived as an approach pointing to new forms of professionalism using evidence for the improvement of professional social work practice and its accountability.