Electrocatalysis facilitates conversion between electrical and chemical energy in fuel cells and electrolysis devices. Rational design of the electrocatalytic interface, including selection of electrode and electrolyte compositions and their optimal structure, requires establishing composition–structure–function relationships. Electronic structure calculations, most typically performed within the framework of density functional theory (DFT), help to develop these relationships by determining how elementary reaction energetics are impacted by electrocatalysis composition and structure. Though DFT methods can explain and predict catalytic behavior at the most fundamental level, they are challenged by difficulties in representing the length and time scales associated with processes at the dynamic electrode–electrolyte interface. In this chapter, we review the approaches used to approximate this interface with DFT for modeling electrocatalytic processes. We first review the challenges associated with modeling this interface, motivating an overview of the various approaches to model solvent and interface electrification. A more detailed emphasis is given to approaches to model the elementary kinetics of the inner sphere electron/ion transfer reactions that dictate activity and selectivity for processes occurring at solid electrode–liquid electrolyte interfaces.