The article is based on an international comparative study in seven European countries, in which informal learning for active citizenship at school was explored by means of in depth case studies. Active citizenship is being recognized as an important goal of education and school pedagogy in an increasing number of countries. After defining the key terms "informal learning at school" and "active citizenship" the conceptual framework on which the study was based is introduced. Next, the most important outcomes of the study are summarized, in terms of core issues that showed varied implementation across countries. These issues are further analyzed in terms of context, input, process and outcome factors, with a strong emphasis on the process factors. Living up to school rules, student participation in school decision making, intercultural conflict and reflective pedagogy were identified as key "process" dimensions, impacting on informal learning for active citizenship at school. In a final section these areas are tentatively worked out as a set of process indicators, applicable in future international comparative studies. (Contains 1 figure and 1 table.)