The purpose of this report is to form a basis and reference material for the deliverables and actions in the ERA4Health Partnership. Most people working in the field of clinical research and clinical trials have experiences and highlighted barriers and bottlenecks to multinational Investigator Initiated Clinical Studies (IICS) but validating these experiences through a literature review is important to have full understanding of what problems investigators, sponsors and participants in clinical trials experience when conducting and participating in clinical studies. The audience we aim to address in this report are first and foremost the partners of ERA4Health, the funders of academic clinical trials in Europe and the European clinical trials infrastructure. However, creating an awareness of barriers and bottlenecks to multinational IICS with all stakeholders in this field is of great importance if we are to be successful in overcoming these barriers. The basis of this report is a literature search, conducted as described in the Methodology section where we aimed to gather information from peer-reviewed original publications, reviews, and reports from 2015 until May 2023. The initial searches yielded over 11,000 papers, but after establishing our inclusion/exclusion criteria, we carried out further in-depth analysis on 223 papers and reports. Many of the results, described barriers and bottlenecks, were as predicted and we compared our results with that of previous reports on the same or similar topics, and found many similarities and some differences. We have structured the report according to the various topics and processes within clinical research, and looked for synergies between them, to identify the actions that will impact the barriers most efficiently. A deliverable for this task was to arrange a workshop, which took place on the 14th-15th of September 2023 in Paris and was titled ‘Analysis of the Bottlenecks and Challenges in Designing and Conducting Multicountry Investigator Initiated Clinical Studies Pillar 2B’. The results from this report were presented at the workshop together with viewpoints from the various stakeholders in academic clinical research across Europe. This was followed by a plenum debate and audience feedback on the topics presented. Viewing the relationships between the barriers, it has become clear that most bottlenecks in multicountry IICS are related to the lack of trained, experienced, and available clinical staff. We find the same with administrative support staff with regards to the planning, setup and conduct of a clinical study. Staff training in the various roles within clinical research and maintaining clinical research support is crucial to be able to carry out successful clinical research. In order to address the barriers of multinational IICS it is important that all stakeholders have a common understanding of the complex management of multinational clinical trials.