Abstract: This is the first part of a two-part report that revisits and updates the verification and validation (V&V) of the Coastal Modeling System (CMS). The V&V study in this part of the report focuses on hydrodynamic and wave modeling. With the updated CMS code (Version 5) and its latest graphical user interface, the Surface-water Modeling System (Version 13), the goal of this study is to revisit some early CMS V&V cases and assess some new cases on model performance in coastal applications. The V&V process includes the comparison and evaluation of the CMS output against analytical solutions, laboratory experiments in prototype cases, and field cases in and around coastal inlets and navigation projects. The V&V results prove that the basic physics incorporated are represented well, the computational algorithms implemented are accurate, and the coastal processes are reproduced well. This report provides the detailed descriptions of those test simulations, which include the model configuration, the selection of model parameters, the determination of model forcing, and the quantitative assessment of the model and data comparisons. It is to be hoped that, through the V&V process, the CMS users will better understand the model’s capability and limitation as a tool to solve real-world problems.