<p>Electrochemical devices such as fuel cells and electrolysers are pivotal to a sustainable energy future, but their commercial viability depends on electrocatalyst stability — a challenge as critical as achieving high catalytic activity. Materials scientists, chemists and engineers need strategies to design catalysts that maintain high performance under demanding real-world conditions. This Review addresses that need by bridging the latest fundamental understanding of nanostructured catalysts with practical application guidelines, offering timely insights into the chemical and structural principles governing catalyst stability — factors that ultimately dictate reliability, longevity and cost effectiveness. We begin by examining how chemical potential drives stability, exploring intrinsic engineering tactics — spanning composition, crystallinity and morphology — as well as extrinsic strategies such as encapsulation, adhesion and microenvironment optimization that protect electrocatalysts under harsh operating conditions. Building on this foundation, we highlight the need for advanced in situ or operando tools that can capture electrocatalyst behaviour in action, thereby enabling further understanding and guiding the engineering of catalyst stability. We conclude with a forward-looking perspective on emerging directions, from stability descriptors to machine learning, that promise to elevate electrocatalyst activity and stability even further. By placing stability at the forefront, this Review hopes to provide a comprehensive perspective for academia and industry, accelerating the development and deployment of robust, economically viable electrocatalysts to facilitate broader adoption of clean energy.</p>