"Development of design principles for electro-chemo-mechanically active oxides" Electro-chemo-mechanically active oxides enable a wide array of energy, processing, sensing, and electronic applications, but limitations in their charge transport, surface reactivity, and chemical expansion hinder efficiency and durability. A fundamental understanding of these point defect-mediated properties needs to be developed in order to enable rapid, rational design of optimized solid state ionics for improved device performance. Particularly, there is benefit in moving beyond conventional electro-chemical studies to consider the coupling between electrical, chemical, and mechanical states of materials, such as the lattice strain occurring upon non-stoichiometric composition changes during operation (chemical expansion). In this talk I will focus specifically on development of design principles for oxygen surface exchange kinetics and the resulting chemical expansion in perovskite-structured ceramics that "breathe." Surface oxygen exchange rates have been measured on model thin films fabricated by pulsed laser deposition, using in situ ac-impedance spectroscopy and a novel optical transmission relaxation technique. Controlled variation of overall film defect chemistry, outermost surface chemistry, and microstructure, has enabled a better understanding of the relative importance of each. Chemical expansion behavior has been studied across multiple length scales using in situ diffraction, thermogravimetric analysis, and dilatometry, with comparison to atomistic computational simulations. Approaches to lower the chemical expansion coefficients (for durability) and increase the surface exchange kinetics (for efficiency) will be discussed.