This book gathers the high-quality papers presented at the 21st International Conference on Computing and Information Technology (IC2IT2025), held on May 15-16, 2025, in Kanchanaburi, Thailand. The book presents an original research work for both academic and industry domains, which is aiming to show valuable knowledge, skills and experiences in the field of computing and information technology. The topics covered in the book include natural language processing, image processing, image processing, intelligent systems and algorithms, as well as machine learning. These lead to the major research directions for innovating computational methods and applications of information technology.