This book gathers the latest advances, innovations, and applications in the field of engineering optimization, presented at the 3rd Engineering and Applied Sciences Optimization (OPT-iii2025), held in Amman, Jordan, on December 18–20, 2025, jointly with conferences OPTARCH2025, ADDOPT2025 and DiGiCES2025. It covers topics such as shape and topology optimization, structural optimization, optimization in micro- and nano-mechanics, lifecycle design optimization and structural health monitoring, multidisciplinary and multiphysics design optimization, multiple criteria decision-making and optimization. Written by leading researchers and engineers, and selected by means of a rigorous international peer-review process, the contributions highlight numerous exciting ideas that spur novel research directions and foster multidisciplinary collaborations.