'The Principle of Materiality as a Generally Accepted Accounting Principle': This thesis deals with the scope and content of the principle of materiality under German accounting and tax law. The relevant German and the European Union legal framework (in particular: Directive 2013/34/EU) is analysed in detail. Particular attention is paid to the principle's power to override domestic rules of accounting and tax law. The thesis addresses the problem of defining materiality and highlights how the principle can be applied. It concludes with a proposal for regulation.