This book includes peer reviewed articles from the 4
th
International Conference on Optoelectronic and Nanomaterials for Advanced Technology (icONMAT 2025), held during 11–14 February in Cochin, India. It highlights recent advances covering a diverse range of themes-including nanomaterials and devices, energy harvesting and storage, thin films and coatings, biomaterials and engineering, ultrafast laser technologies, 2D materials and devices, and quantum materials. It presents latest developments, innovative methodologies, potential applications with the emphasis on solving critical challenges in energy efficiency, healthcare, and quantum materials synthesis. By fostering technology-driven solutions and interdisciplinary collaborations, this collection serves as a valuable reference for researchers, academicians, and industry professionals working in materials science, nanotechnology, and advanced device engineering.