SENSEI Computational Fluid Dynamics Code: A Case Study in Modern Fortran Software Development. This paper discusses the development of a new Computational Fluid Dynamics code under development in the Aerospace and Ocean Engineering department at Virginia Tech. SENSEI is a multi-block, structured grid, cell-centered, second-order finite volume solver developed using agile programming techniques and written in Fortran 03/08. The code base integrates the work of several projects into a single system for performing error estimation and grid adaptation and is designed to provide an easily extensible common framework for future development. In addition, it utilizes a new formulation of the method of manufactured solutions ideally suited for solvers which are based on discretizations of the weak form of the governing equations of interest.