The number of individuals and households that own an additional property beyond their primary home is on the rise in several countries. However, recent studies have been inconsistent in describing such properties, referring, for instance, to the return of private small-scale landlordism, the proliferation of second homes, or the significance of dwellings that are held as investment properties. Rarely are these disparate issues considered together, either theoretically or empirically. This special issue mobilises the concept of multiple property ownership (MPO) to provide a more integrated analysis. In this introduction to the special issue we propose multiple property ownership as a conceptual banner that includes second homes, buy-to-let properties, holiday rentals, intergenerational support properties and safe deposit box properties. While these properties may differ considerably in terms of purpose and use, we argue that they are part of a broader proliferation of property wealth accumulation at the household level. Considering multiple properties together can motivate a deeper understanding of property wealth concentration and changing property relations in the post-crisis context. We introduce a typology of multiple property ownership, discuss the consumption and investment value of different property types, and outline some drivers of multiple property ownership, before considering implications for housing research. We end with a brief discussion of the five articles in this special issue and how they deepen current understanding of multiple property ownership.