Materials with the scheelite structure exhibit mixed ionic and electronic conductivity, and are of interest as oxidation catalysts. Scheelite materials are also possible candidates for use as electrolytes or cathode materials in solid oxide fuel cells. Our work on the scheelite system, based on BiVO4, shows that both ionic and electronic components of the conductivity can be modified by doping this material. Both A and B site doping have been investigated. The A cation was replaced by Ca, Ce and Zr, and the B site by Mo.