Book excerpt: This book presents selected papers from the 7th International Conference on Water and Flood Management,with a special focus on Water Security under Climate Change, held in Dhaka, Bangladesh in March 2019. The biennial conference is organized by Institute of Water and Flood Management of Bangladesh University of Engineering and Technology. The recent decades have experienced more frequent natural calamities and it is believed that climate change is an important driving factor for such hazards. Each part of the hydrological cycle is affected by global climate change. Moreover, increasing population and economic activities are posing a bigger threat to water sources. To ensure sustainable livelihoods, safeguard ecosystem services, and enhance socio-economic development, water security needs to be investigated widely in a global and regional context.