There is reason to believe that environmental policy convergence resulting from policy diffusion is influenced not only by functional imperatives of the world market, but also by a collective behaviour of national governments, where pioneer countries function as (intellectual) leaders under conditions of uncertainty. Their solutions for general environmental problems are adopted by other countries. As a rule, there is one single solution that is preferred by a large group or the majority of countries. This regulatory 'conformism' makes pioneer roles of countries highly relevant. The article analyses the character and role of such 'trend-setters' in environmental policy.A necessary condition for becoming a pioneer country in environmental policy is a high domestic capacity for environmental policy-making. This encompasses institutional, economic and informational framework conditions as well as the relative strength of the green advocacy coalition of a country. While these factors refer to relatively stable factors of policy-making, this does not explain why sometimes countries give up their roles as pioneers. To explain this, an analytical framework is proposed that encompasses situative factors, strategic factors and actor constellations, especially the coalition between organized proponents of environmental objectives and economic modernizers. This coalition of ecological modernizers may break down, for example in times of economic crisis. The political and economic framework conditions of globalization may sometimes bear impediments for pioneers, but at the same time they also provide incentives for highly advanced countries to take over national pioneer roles -at least in the field of environmental protection, which has become an important issue in the competition for innovation.