This paper deals with the management of settlement growth in the Grand Duchy of Luxembourg from the perspective of informality. Luxembourg is subject to high demographic and economic growth pressures across all parts of the country (capital, old-industrialized South, rural North), which strongly challenges the current planning system. At the same time, there is no formal regional planning, apart from approaches of inter-municipal cooperation, which are mainly voluntary in nature. Drawing on empirical case studies in two high-growth municipalities (Junglinster, Schuttrange), the paper outlines planning decisions in the institutional triangle between municipality, state and private institutions. Informality serves here not only to compensate for a lack of planning control, but also to deal with the country’s complex legal framework conditions. The vital interests of landowners come into play informally as well: since parts of the country’s wealth emerge from the valorization of property, speculative interests are immanent, and thus block development processes. In this context, the paper addresses elements of a regional growth management that could close the gap that exists between state planning and municipal autonomy.