The Evolution of Electrochromic Materials: Transitioning from Single‐Metal Oxides to Multimetal‐Based Systems for Multifunctional Smart Devices

Electrochromic materials, which enable reversible modulation of transmittance, absorbance, and reflectance across the UV–Vis‐NIR spectrum, are classic examples of active optical materials. While the field of electrochromism has witnessed explosive growth in multimetal systems over the past two decades, the literature remains fragmented across materials chemistry, solid‐state physics, and device engineering. This review provides the first systematic roadmap of the evolution from single‐metal to multimetal‐based electrochromic materials, addressing a critical gap in the literature across materials chemistry, solid‐state physics, and device engineering. We establish a detailed structure–property–performance framework for transparent conducting electrodes (TCEs), anodic, cathodic, and electrolyte materials, while critically evaluating performance parameters and identifying inconsistencies in reporting to propose standardized protocols. Furthermore, we assess cutting‐edge multifunctional integrations, including electrochromic energy storage, batteries, self‐powered systems, flexible electronics, and thermochromic hybrids, revealing how multimetal designs enhance optical, electrochemical, and mechanical properties. Concluding with a forward‐looking roadmap, we outline four actionable challenges: rational materials discovery via machine learning, metal's criticality and Safe‐and‐Sustainable‐by‐Design, operando interfacial engineering, sustainable fabrication, and IoT integration. This authoritative reference bridges fundamental insights with device‐level performance, accelerating next‐generation electrochromic systems for smart windows, wearable displays, building decarbonization, and intelligent infrastructure.