Anionic-conducting materials, especially oxide ion conductors, have been the focus of continued research efforts over the past decades due to their potential use in renewable energy applications, such as oxygen-permeable membranes and solid oxide fuel cells (SOFCs). A crucial parameter holding back their widespread implementation is the undesirably high temperature at which they show sufficiently high ionic conduction, which even for currently used, best-in-class materials (such as yttria-stabilised zirconia, YSZ) is > 923 K. There is still very much a need to discover and develop novel ionic conducting materials that operate at lower temperatures and to characterise the connection between structure and conductivity in order to move towards rational design of optimal materials. Bismuth oxides and various substituted derivatives have been mined as a rich compositional space within which to find new fast ion conductors, sparked by the extremely high oxygen ionic conductivity values of the cubic δ phase of Bi 2 O 3 , which is not stable at lower temperatures due to transformation to a monoclinic polymorph below 1003 K. Of the families of materials that have been explored, including phases resulting from isovalent doping (rare earth Ln 3+ ) as well as aliovalent doping (such as pentavalent P, V, Nb, and/or Ta), vanadium-substituted bismuth oxides have shown the most promising values of ionic conductivity at relatively lower temperatures. These materials often exhibit complex superstructures; understanding the role the V dopant plays in enabling the superionic behaviour of the Bi-O lattice is correspondingly complex, but is nonetheless necessary in elucidating the best way to optimise these materials for device applications.