This book compiles cutting-edge research from the 2025 International Conference on Mechanical Transmission (ICMT 2025), systematically exploring theoretical breakthroughs and industrial innovations in mechanical transmission. The content spans new transmission theories and modeling methods (e.g., digital twin-driven lifecycle design), smart materials (composites/polymers), green manufacturing technologies, and AI-integrated optimization strategies for transmission systems. The book focuses on addressing core challenges such as fatigue reliability, NVH (Noise, Vibration, and Harshness) behavior, and energy efficiency improvement, while showcasing industrial applications of smart gears and bearings, predictive maintenance algorithms, and sustainable lubrication technologies.