Abstract Large crystals of BiVO 4 were grown. Extensive twinning can be related to the ferroelastic transition at 528K. The structure of BiVO 4 was refined at 4.5, 295 and 566K from powder neutron diffraction data and at 295K from powder X-ray diffraction data by the Rietveld profile technique. Space groups of I4 1 a above and I2 b below 528K were confirmed. It is suggested that the transition in BiVO 4 is driven by the lone-pair cation Bi 3+. The Bi-O polyhedron is regular above the transition but becomes significantly distorted below the transition. This lone-pair distortion increases on cooling from 295 to 4.5K. The V-O tetrahedron remains regular at all temperatures.