This book provides innovative insights while also acting as a comprehensive guide for researchers, engineers, and graduate students in the fields of materials science, metallurgy, and environmental engineering. This book focuses on the innovative development of high-entropy alloys (HEAs), which are multi-principal element materials known for their exceptional strength, corrosion resistance, and thermal stability, while integrating sustainability into their design and application. The main topics include alloy design strategies, energy-efficient processing (including additive manufacturing), waste valorization (e.g., agro-waste reinforcements), microstructural engineering, advanced characterization, and applications in aerospace, automotive, and defense, culminating in a roadmap for scalable production. These topics are crucial for addressing resource scarcity, high production costs, and environmental impact in modern industries. Also, the book provides solutions to the problem of traditional HEA development’s ecological footprint by offering a framework that leverages computational tools, circular economy principles, and low-cost materials, ensuring high-performance solutions align with global sustainability goals.