Intellectual Property (IP) box regimes are aimed to promote R&D&I by granting a tax benefit to those that assign certain intangibles for their exploitation or further development. Notwithstanding this, the regime (classified as an output incentive) has been debatable since the very beginning for being a source of tax avoidance and tax planning. Indeed, the European Commission has identified it as an indicator of aggressive tax planning, and the OECD as a "hot issue" in the scope of the BEPS Action Plan. The agreement on the so-called (modified) nexus approach determines the survival of these preferential tax regimes, but this does not mean IP boxes are a good tax practice. Moreover, it is debatable that a preferential treatment is given from the tax system to intangibles that are already protected by IP rights. The author analyses the justification for this regime from a public finance perspective, its interaction with anti-BEPS measures and its compatibility with EU Law (e.g. EU State aid rules). Finally, the author tackles the relevant design aspects of IP box regimes to be effective in the purpose of increasing business spending in R&D&I. Esta obra completa el catálogo de Thomson-Reuters Aranzadi.