New Environmental Policy Instruments (NEPIs) are increasingly discussed and adopted across countries. From a global perspective a rapid diffusion of these market based, voluntary or informational instruments can be observed. In our article – which is mainly explor-ative in nature – we argue that the adoption of NEPIs by national policy makers should not merely be interpreted as a reaction to newly emerging environmental problems or to real or per-ceived deficits of traditional (command and control) regulation in coping with those problems. To an important degree the use of NEPIs can be ascribed to the inner dynamics of international processes of policy transfer or policy diffusion, which make it increasingly difficult for national policy-makers to ignore new approaches in environmental policy that have already been put into practice in forerunner countries. In a first step, the article outlines the concept of policy diffusion. In a second step, we will de-scribe the trans-national spread of four different NEPIs (Eco-labels, Energy/Carbon Taxes, Na-tional Environmental Policy Plans/Strategies for Sustainable Development and Free- Access-of-Information (FAI) provisions) by showing the respective pattern of spread in empirically based curves. In a third step, the article analyses the underlying mechanisms of policy diffusion. We will argue that in addition to the national demand for adequate environmental policy instruments the spread of policy innovations is influenced by the presence or absence of international plat-forms or promoting agencies, which have placed the advancement of certain NEPIs on their agenda; and by the specific characteristics of the policy innovation itself. Finally, we will draw some preliminary conclusions about the motivations of policy makers to adopt or to reject new environmental policy instruments. We argue that the utilization of a softer and more flexible approach cannot exclusively be explained by the decision makers’ considera-tions of improving the efficiency of environmental policy making. Additionally, considerations of generating legitimacy affect the policy makers’ decisions.