This paper introduces the special issue on the Policies for Ecological Tax Reform: Assessment of Social Responses (PETRAS) project about responses to ecological tax' reform (ETR) in Europe. Although ETR is widely accepted to be a policy with desirable effects, its implementation has been limited by problems of political acceptability. The project aimed to address the question of how to make such a policy more acceptable. It is the first study to examine in depth the thinking of members of the general public about the ETR policies and is also the first international comparative study of the thinking of ordinary business people about ETR policies. The PETRAS project methodology was based around the use of interviews and focus groups to inform the assessment of social responses to ETR policies and the development of improved designs for them. A number of issues emerged relating to awareness, trust, understanding of the purpose, visibility, incentives, regressivity.. levels of taxation. terminology, communication about ETR and the use of alternative instruments. Together with these similarities, a pattern of differences between the countries can also be seen. The final section of this paper introduces the national studies described in the following papers. (c) 2004 Elsevier Ltd. All rights reserved.