Thin capitalization rules have recently been introduced (in Italy and the Netherlands) and subject to reform (in Germany and the United Kingdom) or may well be amended in the near future (in France). Such rules have also been the topic of significant judicial procedures (the ECJ Lankhorst-Hohorst case). This special issue of "European taxation", the guest editor of which is Bruno Gouthière, examines these issues and places them in context by way of a comparative survey of the thin capitalization rules in 29 countries (the 25 member states of the EU, plus Norway, Russia, Switzerland and the USA).