Abstract. In the literature, many seemingly contradictory structure models of boulangerite, ideally Pb 5 Sb 4 S 11 , and the related mineral falkmanite have been reported. These can be explained by a phase transition between a low-temperature (LT) modification (P2 1 /c, a ≈ 8.07 Å, b ≈ 23.5 Å, c ≈ 21.6 Å, β ≈ 100.7°) and a disordered hightemperature (HT) modification [Pnma, a = 23.530(2) Å; b = 4.0385(8) Å and c = 21.273(2) Å, R 1 (obs) = 0.039] that occurs above ca. 350-400°C. The almost completely ordered distribution of lead and antimony cations in the LT modification involves a superstructure; the corresponding reflections are obvious in electron and X-ray diffraction patterns. Partial ordering may render them more or less diffuse. They vanish upon heating above the transition temperature, also for originally ordered natural boulangerite (from Trepča, Kosovo), and appear again after annealing below the phase transition temperature (e.g. at 330°C). The HT phase is characterized by pronounced cation disorder. Cation ordering can be described by group-subgroup relationships which may also serve for a unified description of various structure models from literature. Starting from the orthorhombic HT phase, a