Cross-border cooperation between tax authorities based on the EU Directive on Administrative Cooperation has been steadily expanded and intensified in recent years. This development is accompanied by numerous interferences with fundamental rights. However, the doctrinal foundations of fundamental rights in the area of tax enforcement within the European Union have so far received little systematic scholarly attention. Thomas Sendke examines this issue by analyzing fundamental rights protection in cross-border European tax enforcement and first determines the applicable fundamental rights standard of review. Clarifying the doctrinal interaction between the various fundamental rights regimes requires, in turn, an analysis of the current state of harmonization in tax enforcement. This reveals that EU fundamental rights already apply in many areas of (cross-border) tax enforcement. The author then compares the protection offered by the different fundamental rights regimes with regard to procedural burdens, before assessing specific tax enforcement measures against the standards he has developed. The analysis shows that, in many areas of cross-border tax enforcement, both Union and national fundamental rights already guarantee a sufficient level of protection - supported in part by recent case law of the CJEU. In other areas, however, fundamental rights protection remains inadequate. Overall, Thomas Sendke's work makes a significant contribution to the emergence of a European tax constitutional law.