_Multifunctional Carbon Nano-Onion Based Nanocomposites: Synthesis, Properties and Applications_ is a comprehensive guide that delves into the structure, design, fabrication, and functional characteristics of carbon nano-onions (CNOs) and their applications in nanocomposites. The book covers timely and significant advances in the field of CNOs, highlighting their unique microstructural, electrical, thermal, mechanical, tribological, and biological properties. It provides a detailed examination of CNOs' roles in various matrices, including thermoplastics, thermosetting polymers, conjugated polymers, rubbers, metals, and metal oxides. Key topics include environmental sustainability, energy storage and conversion (such as solar cells and lithium-ion batteries), electronic applications (sensors), and biomedical applications. In addition, it discusses the challenges and opportunities faced by researchers in the field and the industrial-scale production and economic aspects of these materials. The structure is organized to first introduce the fundamental aspects of CNOs and then progressively dive into specific applications and future prospects. It is intended for researchers, engineers, and academics interested in nanotechnology and nanocomposites, serving as a vital resource for understanding the evolving landscape of CNO nanocomposites and their wide-ranging applications in modern science and technology. • Provides a comprehensive exploration of carbon nano-onion and their nanocomposites with extensive coverage of synthesis, properties, and applications • Offers a detailed analysis of nanohybrid categories with various matrices • Highlights the technological applications of carbon nano-onion nanocomposites spanning multiple industries related to environment/sustainability, energy/electronics, corrosion/radiation protection, health, and biodegradation • Examines the future status and challenging industrial perspectives of carbon nano-onion nanocomposites