High-entropy alloys (HEAs) have materialized as a versatile class of materials in electrochemical applications, offering an ample space for tuning catalytic and electrochemical properties. This chapter delves into the fundamental principles governing Heas, commencing with an introduction to their multi-component architecture and the core effects—high configuration entropy, lattice distortion, sluggish diffusion, and the “cocktail” effect—that distinguish them from traditional alloys. The chapter explains various synthesis strategies which are critical for exploiting these materials in various areas of research. The chapter then focussed to the cutting-edge applications of HEAs in electrochemical sensors and supercapacitors, highlighting how multi-element synergy and electronic structure modulation for biomolecules, environmental pollutants etc. and high specific capacitances and exceptional cycling stability. Another focus of this chapter is the superior performance of HEAs in electrocatalytic reactions, where the synergetic effects of multi-element facilitates exceptional activity and stability in the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction, with developing progress in other electrocatalytic reactions. By bridging the gap between structural complexity and electrochemical performance, this chapter highlights the potential of HEAs as a platform for next-generation energy storage, electrochemical sensing technologies and electrocatalytic applications.