The electrochemical CO 2 reduction reaction (CO 2 RR) has emerged as a promising approach for sustainable carbon cycling and valuable chemical production. Various methods and strategies have been explored to boost CO 2 RR performance. One of the most promising strategies includes the construction of stable ionic interfaces on metallic or molecular catalysts using organic or inorganic cations, which has demonstrated a significant improvement in catalytic performance. The stable ionic interface is instrumental in adjusting adsorption behavior, influencing reactive intermediates, facilitating mass transportation, and suppressing the hydrogen evolution reaction, particularly under acidic conditions. In this Perspective, we provide an overview of the recent advancements in building ionic interfaces in the electrocatalytic process and discuss the application of this strategy to improve the CO 2 RR performance of metallic and molecular catalysts. We aim to convey the future trends and opportunities in creating ionic interfaces to further enhance carbon utilization efficiency and the productivity of CO 2 RR products. The emphasis of this Perspective lies in the pivotal role of ionic interfaces in catalysis, providing a valuable reference for future research in this critical field.