MFEM is an open-source software library that provides advanced mathematical algorithms for use by scientific applications. By relying on MFEM, application scientists can quickly develop highly accurate physics simulation codes on a variety of platforms—from laptops to the world’s largest supercomputers. MFEM version 4.0 incorporates the most advanced techniques from the scientific computing research community, and its methods are widely applicable, highly impactful, and easy to use. A new video (7:07) features members of the LLNL development team, who describe how the software library works.