This book presents a curated collection of cutting-edge research and practical insights into one of the most pressing global challenges of our time: securing water under a changing climate. Framed around the need for adaptive strategies to foster sustainable and resilient development, it explores the multifaceted dimensions of water security through an integrated lens that bridges science, policy, and practice. Structured into eight thematic parts, each part comprises multiple chapters contributed by leading researchers and practitioners from around the world, offering a rich tapestry of perspectives, methodologies, and real-world experiences. The book intentionally balances technical rigor with policy relevance and practical application, making it a valuable resource for academics, decision-makers, and frontline practitioners alike. It is designed to inspire informed decisions, drive innovation, and catalyze transformative change toward water-secure and climate resilient futures.