In the past several years, computational models for free surface flow simulations have been increasingly in demand for engineering, construction and design, legislation, land planning, and management decisions. Many computational models have been hastily developed and delivered to clients without the proper scientific confirmation and certification. In order to correct this, the ASCE/EWRI Task Committee developed a new rigorous and systematic verification and validation process, Verification and Validation of 3D Free-Surface Flow Models, which discusses this procedure in detail. The topics include terminology and basic methodology; analytical solutions for mathematical verification; mathematical verification using prescribed or manufactured solutions; physical process validation; application site validation; the systematic model verification and validation procedure; systems analysis considerations, findings, and conclusions; and recommendations. The appendixes contain input data for test cases and formulations and codes for manufactured solutions. This publication will be indispensable for students and professionals working on computational models and environmental engineering.