Most scholarship in spatial planning presupposes an established institutional setting, where a specific legal framework is in place, one is accustomed to certain procedures and routines, and planning has a certain (national) history. In cross-border regions, however, this becomes problematic as different institutional settings clash. Combining systems and organizational theory, this article constructs a theoretical perspective on planning, explicitly conceptualizing differences, that is, boundaries, in institutional settings. This sheds new light on the prospects and realities of spatial planning across national borders. National borders double the complexity of spatial planning, and organizations working in cross-border spatial planning need to take this into account by acknowledging their own and others’ organizational boundaries as well.