Have New Public Management (NPM) reforms in public organizations improved the quality, efficiency and effectiveness of the delivery of public policies? NPM reforms, understood as a style of organizing public services towards the efficiency and efficacy of outputs, have been controversial. They have been accused of importing practices and norms from the private sector that could collide with core public values, such as impartiality or equity. Yet, with few exceptions, we lack systematic empirical tests of the actual effects that NPM reforms have had on the delivery of public services. In this introductory article, we summarize a special issue devoted to cover this gap. And, overall, we find that neither the catastrophic nor the balsamic effects of NPM reforms are confirmed, but the success (or failure) depends on the administrative, political and policy context those reforms take place.