Ceria and its derivatives find use in a wide variety of technologies from traditional applications in solid oxide fuel cells, catalysis, and electrochemical sensors, to new applications in computing, medicine, and water splitting. The suitability of ceria for these many applications derives in part from the redox flexibility of the material, with the predominantly Ce⁴⁺ ion adopting the 3+ oxidation state under conditions amenable to external control. The very high oxygen ion transport in suitably doped ceria is a second critical factor driving its technological value. Here we present recent results highlighting transport and redox activity in (i) bulk, (ii) grain boundary, and (iii) surface regions of ceria, obtained using a range of techniques from bulk thermogravimetric measurements, to in situ X-ray absorption studies and electron holography. We report on the unusual behavior of ceria upon substitution of Ce with the nominally isovalent species Zr. Contrary to what might be expected, Zr⁴⁺ has a dramatic impact on oxygen vacancy formation, in both the bulk and surface regions of the oxide. We further report on the dramatic role of trace impurities on transport across the grain boundaries of polycrystalline, rare-earth doped ceria. The insight garnered suggest new approaches to controlling material behavior for optimal technological characteristics.