The levying of withholding taxes on non-residents by the source state is a long-standing topic in EU tax law. The recent case Brisal and KBC Finance, concerning a withholding tax levied on an outbound interest payment, constitutes just the last addition to the line of judgments on this issue rendered over years by the Court of Justice of the European Union. In Brisal the Court first confirmed that Member States are permitted to use different techniques for charging a tax on residents and non-residents for the same item of income, i.e. through a final-year assessment and an immediate retention upon the payment. However, the judiciary of Luxembourg found that residents and non-residents are in a comparable situation with respect to the deductibility of operational costs and thus both categories shall be treated equally in this regard. Although this conclusion could most likely have been anticipated in light of precedent decisions of the Court, the judgment in Brisal is equally remarkable since it disrupts a fundamental tenet of taxation of income earned by non-residents without a permanent establishment, i.e. that the source state can levy a withholding tax on the gross amount of such income and that the expenses of the underlying activity have to be considered by the residence state. Besides and more generally, the decision confirmed that the CJEU is increasingly willing to scrutinize the methods for calculating the tax base adopted by Member States in cross-border scenarios.