This book presents selected contributions of the 9th International Conference on Water Resource and Environment (WRE 2023) which is held in Matsue, Japan, November 21-24, 2023. The book discuses a wide range of topics, including Hydraulics, Hydrology and Water Resources Engineering, Environmental Engineering and Sustainability, Indoor Environments, Risk Analysis, Safety and Security, Ocean and Offshore Engineering; Ships and Floating Structures, Coastal Engineering. The chapters in this book are very useful to professionals and academicians for improving their work practice.