This article first provides an overview of the concept, categories and objectives of joint audits, defined as all forms of international cooperation between tax authorities where officials from one country take part in a tax audit carried out by officials of another country. Subsequently, questions of applicable law, taxpayer rights standards in particular, are discussed. On this basis, an in-depth analysis of the relevant constitutional and legal guarantees of taxpayer rights is carried out from the specific perspective of EU law. The article concludes with a plea for further harmonization of joint audit procedure at EU level, in order to provide legal certainty and as a prerequisite for a more prominent role of this legal instrument.