Theoretical modeling offers a gauge to identify the role of atomic-scale factors in controlling observable charging/discharging rates and, thus, enables formulation of fundamental engineering principles. Butler-Volmer (BV) theory has traditionally been used to model interface charge transfer kinetics, where the classical physics-based BV is considered to reflect cases where ion transfer (IT) steps are rate limiting. In contrast, the influence of electron transfer (ET) on charge transfer kinetics, as described by Marcus-Hush-Chidsey (MHC) theory, has lately been highlighted for both Li + intercalation as well as conversion electrodes. In the more general case, mixed IT and ET rate control can be expected, motivating the recently introduced theory of coupled ion-electron transfer (CIET). In CIET, IT and ET are assumed to occur simultaneously along a shared reaction coordinate, where the description of IT in the classical rather than quantum regime distinguishing CIET from the related theory of coupled proton-electron transfer (CPET). Similar to BV-and MHC-based approaches, the parameters needed for CIET can be directly evaluated from atomistic and first principles modeling, including solvent reorganization energy (𝜆), electronic coupling (𝐻 DA ) between donor and acceptor states, as well as ion adsorption (𝜔 𝐿𝑖 +) and ion transfer (𝛽) energies. While the dynamic nature of the interfaces can be captured using enhanced sampling molecular dynamics (MD) techniques, the CIET parameters are derived from first principles calculations conducted at constant charge states in order to probe the free energy landscape before and after charge transfer-accessible via, e.g., constrained density functional theory (cDFT). In addition, to reflect experimental conditions and to minimize the influence of finite cell-size effects, the calculations should be carried out at constant electrode potential (i.e., constant electron chemical potential or Fermi level), which can be achieved via electrochemistry-adapted DFT using, e.g., grand canonical potential approaches. The CIET theory, hence, outlines a generally applicable framework that links atomic scale properties to battery performance, allowing for independent first principles evaluation of experimentally derived data as well as for in silico-guided materials design.