This book presents a diverse collection of research contributions from the 9th International Congress on 3D Printing Technologies and Digital Industry 2025 (3DPTC2025), showcasing the rapidly evolving landscape of additive manufacturing, digital design, and smart production. Covering innovations ranging from advanced materials-such as nanoparticle-reinforced composites, recycled polymers, PEEK, and metal powders-to AI-driven process optimization and real-time defect detection, the chapters highlight progress in mechanical engineering, sustainable manufacturing, biomedical applications, and industrial integration. The book features studies on renewable-energy-powered systems, improved thermal and structural performance, immersive VR-based educational tools, and design strategies for next-generation 3D printing. With additional insights into environmental reuse, cultural heritage preservation, and emerging manufacturing tolerances and standards, this collection offers a comprehensive view of the scientific, technical, and societal dimensions shaping the future of additive manufacturing.