Interface management (IM) is an emerging construction management practice that is mainly concerned with the integration effort of (mega)projects through the management of project interfaces. Even though a plethora of benefits is attributed to IM, a clear overview of how to effectively manage interfaces is non-existent. Without a general understanding on what IM entails, false expectations about its use are created. At the same time, IM developments from academic research are facing obstacles in their adoption in practice, for practitioners are often not represented in these developments. The absence of situated knowledge (i.e. knowledge found and created in practice) in IM development is problematic, for a profession, or professionalism in general, builds on a body of knowledge comprised of integrated knowledge from theory and practice. For this reason, this research has attempted to take a step in the professionalisation of IM by converging the knowledge from theory and practice. That is, enriching the professional content by creating uniformity on the concept of IM and its key principles. The following research question underpinned this effort: What step can be taken in the professionalisation of IM, based on the perspectives from theory and practice? For this, the theoretical perspectives on IM and its professionalisation were studied first, by means of a literature review. Then, practitioner perspectives were studied on the same topics through semi-structured interviews with twelve practitioners involved in the different domains of integral project management. These practitioners were all employed by a large Dutch engineering and consultancy firm. The gathered data was then subject to thematic analysis. A comparison of the findings revealed a similar dichotomy in IM in both theory and practice: a distinction between the technical and organisational aspect. As the results showed possibilities for professionalisation from both sides, it was argued that professionalisation should ultimately happen on both fronts. To create a basis for professionalism, an appropriate means to integrate the theoretical and situated knowledge needed to be found. To this end, literature on the professionalisation of related construction management disciplines was consulted. Inspired by the professionalisation of risk management, a set of key principles was deemed an appropriate medium to integrate the theoretical and situated knowledge of IM. Hence, a rough guide to IM has been created containing key principles. These principles have been validated by two IM experts in separate validation interviews. Concluding, the development of a set of key principles of IM is the answer to the research question, which in itself provides a step towards professionalisation. Uniformity on the topic has now been created by the convergence of knowledge from theory and practice. The principles thereby lay a foundation for (professionalism in) conducting IM, while leaving room for customisation at the same time. Practitioners from the different roles of integrated project management are recommended to use the principles at the start of (infrastructure) construction projects to create an understanding of interfaces and IM in general. It is believed that in this way the established uniformity on paper can be translated to practice.