Executive summaryOn 14 May 2020, the Court of Justice of the European Union (CJEU) concluded that certain features of Luxembourg’s fiscal unity regime in both its pre-2015 and post-2014 versions do not comply with the European Union’s (EU) freedom of establishment principle.The case concerns questions surrounding “horizontal fiscal unities,” i.e., fiscal unities between sister companies, and relates both to the Luxembourg fiscal unity regime before 1 January 2015 (i.e., at a time when the law only allowed “vertical fiscal unities”, i.e., fiscal unities headed by a common Luxembourg parent company or permanent establishment) and after the introduction of the possibility of...