Over the last decade, we have been making monodispersed nano-crystals of oxides and studying their structure and stoichiometry changes as a function of crystal-size. Today we are studying their thermal expansion and resistance to compression (bulk modulus) as a function of crystal-size. The surface of a nano-crystal with its gaseous environment is a special type of interface, probable the simplest and most easily controlled at least on the gaseous side. In a flat-form, these “interfaces”, which are surfaces, are accessible to surface probes such as scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) and are providing a way to investigate them. When nano-oxide crystals are modified by a dispersed surface decoration of metal nanoparticles or by direct doping of metal ions into the oxide lattice, many possibilities arise, particularly in catalysis. Earlier, oxide-supports were usually considered inert with the sole purpose of supporting the dispersed metal nanoparticles to avoid their coarsening during heat-exposure. Later, it was discovered that some oxide supports such as ceria, zirconia and their binary oxide alloys can play an important role in the redox reactions by supplying oxygen in one cycle and absorbing excess oxygen in another. The nano-oxides’ lattice oxygen is available for oxidation and their oxygen vacancies are ready to take up oxygen for reduction. Nano-crystals form many grain boundaries and numerous interfaces when they are consolidated in a bulk form such as pellets or prepared in thin films. Their transport properties are drastically different from bulk forms with micron-size grains. Resistance at interfaces and grain boundaries to ionic transport from Debye-layer- potential barriers disappears when the crystal-sizes are comparable to the Debye-layer thickness. Our earlier work on impedance spectroscopy and microstructure of yttria-doped ceria thin films demonstrates this. This approach to study grain boundaries is different from our bi-crystal approach where only one boundary is being studied at one time. This assembly approach is appropriate for fine-grain oxides and actually more suitable because the space-charge-layers in these fast-ionic oxides render the local atomic structure somewhat less important.