The report summarizes information on indoor pollution by nitrogen dioxide (NO2) In European countries participating in the concerted action "Indoor Air Quality and Its Impact on Man" (COST project 61 3). Major scope of the report IS to give concise information to people involved In research planning, policy making and regulatory activities and to help to identify a European view of the issue. The summary includes a short review of health effects of NO2 and of existing air quality guidelines and standards. For those countries for which information has been made available the more important sources, occurring indoor concentrations and national polices have been collated. Preventive measures are briefly discussed and research needs are identified.