In the field of electrocatalysis, significant emphasis has been placed on developing electrode materials to enable critical energy storage reactions and sustainable chemical synthesis. However, the electrode is just one part of a complex interfacial environment that controls substrate adsorption and reactivity. In the presence of a liquid electrolyte and an electrochemical interface, adsorption processes behave substantially differently than those in the gas phase. Understanding these adsorption processes, which play an important role in all electrocatalytic reactions, is critical for the design of effective electrocatalysts. In this Perspective, we discuss the current understanding of electrochemical adsorption and its implications for catalyst design.