Cerium oxide is one of the most studied mixed ionic and electronic conductors. In this talk, I will present a systematic study of the oxygen capacity of ultrathin ceria films under significant compressive and tensile strain, starting at a thickness of 1 nm. Coherently strained ceria thin films were grown on various single-crystalline substrate substrates via pulsed-laser deposition. Using in-situ electron diffraction and high-resolution transmission electron microscopy, the precise thickness at which the growth transitions between 2-D growth, 3-D island growth and plastic deformation through the creation of misfit dislocation is identified. The redox capacity of the ultrathin ceria films were characterized using ambient pressure X-ray photoelectron spectroscopy, which exhibits an ununsual dependece on misfit strain.