For Europe's urban agglomerations to be economically competitive, it is vital that international destinations be easily accessible. Although much has been invested in the construction of European rail infrastructure over the past century, passenger transport by rail has not grown as fast as transport by road and air. So why do people not use international trains more, even though they have an extensive international rail network at their disposal? Based on a series of in-depth interviews with relevant public and private stakeholders and two expert meetings, we identify the main bottlenecks and constraints. In order to understand the complexity of international rail transport, we have divided the existing bottlenecks into four groups corresponding to four layers of the rail transport system: mobility services, transport services, traffic services, and the physical and digital infrastructure. We formulate concrete policy recommendations for improvements to be made in the various components of the rail transport system.