Mixed metal oxides are ionic compounds containing at least two metal ions within an oxide structure. The literature contains a plethora of examples of mixed metal oxides on the bulk scale, which have been well characterised, however, mixed metal oxides on the nanoscale are far less well understood. The work presented here investigates the Bi2O3-CeO2-Nb2O5 mixed oxide system and characterises the resulting nanoparticles and crystal structures. Although the parent oxides are well known and much work has previously been done in analysing their crystal structures, combinations of these oxides have not been well characterised, especially on the nanoscale. Using high resolution electron microscopy (HRTEM), powder X-ray diffraction (PXRD), electron dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) as analytical tools, the structures of the nanoparticles in this system have been explored. As each of the parent oxides possess useful properties, which have been utilised in industrial applications such as electrolyte components in solid oxide fuel cells and as catalysts in a range of chemical reactions, it was hypothesised that if all three metal ions could be contained in one particle they could show novel and interesting characteristics. It was proposed that due to the more relaxed crystal structure in nanoparticles, the solid solubility of the metal ions should be increased, and a solid solution of ions would form. This work presents results showing the synthesis of binary and ternary oxides in the nano-form within the Bi2O3-CeO2-Nb2O5 system, including quantitative analysis of these particles. Secondly, and most importantly, it presents the first successful synthesis of quaternary oxide nanoparticles containing bismuth, cerium and niobium using the low temperature resin-gel method. Finally, the work attempts to explain how and why the ions are ordered in a given arrangement, with bismuth showing a preference for surface site occupation, as shown by XPS data, and describes some preliminary computational results which corroborate the experimental data.