While Advanced Therapy Medicinal Products (ATMPs), a European legal classification of medicinal products based on genes, cells and tissues, raise specific quality issues, the latter are particularly acute in the context of clinical trials of ATMPs. In comparison to more traditional medicinal products, ATMPs have been subject to specific regulatory provisions in the European Union (EU) since 2007. In addition, many new guidelines have also been adopted to consider the issues raised by ATMPS. Most importantly for investigational ATMPs, the European Commission has adopted and published Guidelines on Good Clinical Practice specific to ATMPs in 2019. Not only are these guidelines targeting ATMPs, they also have a dedicated section on investigational ATMPs exploring the particular challenges raised when tissues and cells of human origin, are administered to a human trial subject, including when ATMPS incorporate medical devices, or delivered with the aim of reconstituting a given bodily tissue or organ. The aim of this poster is to highlight the specificity of quality requirements of investigational ATMPs by examining the dedicated subsections in the guidelines published by the European Commission and analysing them through the lens of the corresponding scientific literature. On the basis of the identification of the specific requirements regarding the quality of investigational ATMPs, the poster will reveal why they raise specific challenges and why these challenges deserve separate regulation in order to demonstrate quality in clinical trials.