Using combined X-ray single crystal and neutron powder thermodiffraction data, the crystal structure of the high temperature γ-form of Bi 4 V 2 O 11 was confirmed and accurately refined in the I4/mmm space group and that of the β-form was entirely determined in the centrosymmetric Amam space group. The two-fold superlattice characterising the β structure is the result of an ordering process involving corner-sharing V–O tetrahedra and disordered trigonal bipyramids. A possible scheme for the γ↔β phase transition is proposed.