Understanding how currents and waves exert force on solid structures is at the heart of many engineering problems CHL faces. More generally, we must understand coupled fluid-structure systems where momentum and energy are exchanged along moving interfaces between the solid structures, water, and air. CHL develops and maintains advanced computational modeling tools for FSI and conducts research in a range of areas that support continued advances in FSI modeling: numerical analysis, scientific computing, engineering mechanics, and mathematical modeling. Since computational modeling is not sufficiently reliable in many cases, especially those involving complex fluid-structure systems, CHL also develops and maintains an array of experimental facilities (flumes and basins) and field data collection capabilities, which are used to study processes, validate computational models, and design structures and vessels. In support of FSI simulation, we also conduct specialized research and development into experimental methods, data acquisition, and field data collection to advance our capability to measure more complex processes and achieve higher accuracy with new measurement techniques.