Das Abzugsverbot des § 4j EStG

National deduction restrictions are considered a key instrument in combating aggressive tax planning and harmful tax competition. Based on the license barrier, the thesis shows which EU and constitutional hurdles unilateral defensive measures must overcome. The focus is on the question of the extent to which deduction restrictions are justified as an instrument for combating harmful tax competition. On the basis of a tax-systematic analysis and an in-depth evaluation of the case law of the ECJ and the Federal Constitutional Court, it becomes clear unilateral national measures are only permissible within narrow legal limits. The standards obtained are also important for future deduction restrictions.