The multiblock method, known by various names such as the zonal method or domain decomposition method, offers a systematic approach to tackle large-scale, intricate problems by breaking them down into smaller, more manageable sub-problems. Each sub-problem is then addressed individually, taking into account their interconnections to ultimately arrive at a comprehensive solution. This book provides a cohesive overview of the multiblock method's principles, particularly in the context of fluid flows, encompassing diverse fields like aerospace engineering, civil engineering, physical oceanography, and even machine learning. It delves into the foundational mathematics, presents model problems, elucidates numerical algorithms, and offers practical examples relevant to fluid dynamics. With its comprehensive coverage, this book serves as a valuable resource for both learners and practitioners, catering to students, researchers, and modelers alike, whether as a textbook for structured learning or as a reference for applied problem-solving.