The aim of this U4 Issue paper is to identify and discuss major challenges, appropriate responses, and relevant tools for addressing corruption in revenue administrations. This text is part of the output from the U4 Focus Area on Public Financial Management and Corruption. How does corruption affect revenue collection, and what are the consequences for development indicators such as growth and poverty? This paper explores the driving forces behind fiscal corruption in order to facilitate a thorough understanding of the problem - a prerequisite for anyone who wants to succeed in designing appropriate measures to improve the situation.