This monograph aims at presenting a unified approach to numerical modeling of tsunami as long waves based on finite difference methods for 1D, 2D and 3D generation processes, propagation, and runup. Many practical examples give insight into the relationship between long wave physics and numerical solutions and allow readers to quickly pursue and develop specific topics in greater depth. The aim of this book is to start from basics and then continue into applications. This approach should serve well the needs of researchers and students of physics, physical oceanography, ocean/civil engineers, computer science, and emergency management staff. Chapter 2 is particularly valuable as it fully describes the application of finite-difference methods to the study of long waves by demonstrating how physical properties of water waves, especially phase velocity, are connected to the chosen numerical algorithm. Basic notions of numerical methods, i.e. approximation of the relevant differential equations, stability of the numerical scheme, and computational errors are explained through application to long waves. Finite-difference methods are further developed in major chapters to deal with complex problems that arise in the study of recent tsunamis.