This paper forms part of a series of analytical pieces on the absence of EU-coordination regarding aggressive tax planning and its effects, prepared by Policy Department A at the request of the ECON Committee of the European Parliament. It provides some background to the political debate and to the efforts which are currently underway to reform the tax system both at an international level, through the Base Erosion and Profit Shifting (BEPS) project led by the OECD and the G20, as well as at an EU level. It describes the basic structure and the fundamental flaws of the current international tax system. A number of techniques and mechanisms have been and are used by modern multinational enterprises (MNEs) for aggressive tax planning purposes. It also illustrates that these structures exploit the interaction of the tax systems of different states. The paper concludes with a description of the key features and role of the Platform for Tax Good Governance, Aggressive Tax Planning and Double Taxation.