Advanced Therapy Medicinal Products (ATMPs), a European legal classification of medicinal products based on genes, cells and tissues, raise specific issues in the context of clinical trials. In comparison to more traditional medicinal products, ATMPs have been subject to specific regulatory provisions in the European Union (EU) since Regulation (EC) n°1394/2007. Yet for the clinical trials with ATMPs, the general regime laid out in Regulation 536/2014 on clinical trials (which came into effect on 31 January 2022) applies, together with the ICH E6 Guidelines on Good Clinical Practice (GCP). For clinical trials conducted in the EU, compliance with GCP is mandatory. The European Commission has also adopted and published 2019 Guidelines on GCP specific to ATMPs, as required by Article 4 of Regulation (EC) n°1394/2007 on ATMPs. These guidelines both adapt the ICH guidelines to ATMPs’ characteristics and provide additional measures that have been considered necessary. However, they are not exhaustive as they explain only some specificities of ATMPs and they remain complementary to the general rules. After having analysed these documents, we will highlight the specificity of requirements for investigational ATMPs in order to reveal the specific challenges they are addressing and why these challenges warrant separate regulation in order to obtain clinical trials’ authorisation for investigational ATMPs.