In this chapter, Ana Paula Dourado analyses the concepts of aggressive tax planning and harmful tax competition that have increasingly influenced EU tax policy over the past 20 years. The chapter first sets out to examine the meaning of aggressive tax planning in light of relevant EU policy documents and legislation such as the ATAD and the Directive on Administrative Cooperation and their interaction with international efforts coordinated at the level of the G20/OECD pursuant to the BEPS project. Going beyond a mere assessment of the legal texts, the author also explores jurisprudential developments concerning aggressive tax avoidance and legislative proposals, especially as triggered by the challenges of digitization. The chapter then focuses on the soft law instruments developed by the EU to respond to harmful tax competition, in particular the 1997 Code of Conduct and more recent efforts to combat tax havens via the EU blacklist. The author concludes that, though distinct, the concepts of aggressive tax planning and harmful tax competition are closely related in that the former is at least partly encompassed in the latter.