Multi-campus university systems are not a new phenomenon. In their foundational analysis of multi-campus universities in the United States published in 1971, Lee and Bowen noted that almost 40% of American students were enroled in institutions that were part of multi-campus systems. The role of these complex multi-campus systems has continued to grow, though they have received surprisingly little attention in the academic literature (Gaither, 1999). In addition to the United States, multi-campus universities have become an integral feature of higher education systems such as the United Kingdom, Australia and South Africa. Their emergence is either a result of predetermined efforts by policy makers or institutional leaders to spread activities across multiple geographies, or the outcome of amalgamation processes involving higher education institutions located in different localities. Yet, despite the adoption of multi-campus university systems in many jurisdictions, surprisingly little is known about the inner workings and key challenges facing these complex systems. This special issue takes an important step towards addressing this knowledge gap. In so doing, it brings together contributions emanating from a multiplicity of national higher education systems, shedding light on key aspects associated with both formal and informal structures, as well as the tensions and dilemmas facing contemporary multi-campus university systems. What is more, both conceptualisation and theorisation in and around multi-campus university systems has been largely neglected, and this is also an aspect that this special issue aims to address. Each author was free to approach a specific case(s) from a particular conceptual or theoretical perspective, thus providing a rich variety of perspectives on the complexity surrounding multi-campus university systems. Taken together, the contributions provided here underline the need for a more sophisticated conceptual and empirical analysis underpinning the emergence and development over time of multi-campus university systems. They also point to the need to approach multi-campus university systems from a more holistic and comprehensive perspective, as one of the many elements composing a complex ecosystem that includes: (1) formalised structures and arrangements, including mechanisms designed by both the state or the "superstructure" (Clark, 1983) and university leadership ("middlestructure") at various levels; (2) informal cultures and deeply institutionalised values, identities and traditions, which make each university and its respective campus constellations somewhat unique in their own right (Clark, 1992); and (3) social networks involving a multiplicity of internal and external actors or stakeholders, from whom both strategic resources and legitimacy are drawn from (Pinheiro, 2015). All in all, the contributions composing this special issue provide new insights on the inner workings of multi-campus universities, not least with respect to the multiple challenges and tensions facing both managers and academics involved with such systems.