The rare-earths (lanthanides + group III) are critical materials that underlie numerous technological advances ranging from information storage, human health, high-performance electronics, energy and the environment, and catalysis. Robust connections between molecular structure, properties, and function are central to advancing the performance and sustainability of these materials; however, achieving this can be limited by the complexity and heterogeneity in homogeneous and heterogeneous systems alike. In this talk, I will share my group’s recent advances in the fundamental understanding and applications of rare-earths in multi-step, multi-electron processes involving oxygen. First, I will describe how 'simple' Lewis acids can interact with transition-metal reactive oxygen species to stabilize rare bio-inorganic intermediates and control both activity and selectivity in (electro)catalytic oxygen reduction, and highlight key design features and quantitative relationships underlying these processes. Second, I will share our efforts focused on the chemistry of rare-earth reactive oxygen species. Access to novel, discrete molecular species provides clear connections between the structure, properties, and reactivity of proposed reactive intermediates invoked in a wide range of heterogeneous and homogeneous processes. Finally, this has enabled our development of stoichiometric and (electro)catalytic processes which break traditional selectivity and scaling relationships, and avoid common parasitic reactions typically observed in other parts of the periodic table.