The Mutant Mouse Resource and Research Center (MMRRC) is a program of the National Institutes of Health (NIH) that strives to expand and ensure access to well-defined, high-quality rodent models for biomedical research. Supported by ORIP’s Division of Comparative Medicine and aligned with ORIP’s 2016‒2020 Strategic Plan to develop novel models of human diseases to study, understand, and eventually cure complex diseases, the MMRRC consists of four centers (at the University of California at Davis, University of Missouri, University of North Carolina at Chapel Hill, and The Jackson Laboratory) that operate as a central repository to accept, cryopreserve, maintain, and distribute mutant mouse strains. By accepting reagents from researchers, the MMRRC promotes an environment of responsible conduct of research, where scientists are obliged to share their resources with each other, which minimizes costs and time associated with the distribution of reagents. From 2010 to April 2017, the MMRRC received more than 8,633 orders from investigators. The MMRRC saves scientists time and costly efforts of having to house, breed, rederive, and characterize mice and conduct duplicative studies due to unexpected phenotypes and experimental variability. The MMRRC now offers next-generation gene sequencing technology of gut microbiota in mice to better equip researchers to conduct reliable and reproducible science, and to avoid unexpected study results. In 2016, the NIH funded the second phase of the newly developed Common Fund’s Knockout Mouse Project (KOMP 2) to make more than 3,000 new genetic knockout mice available through the MMRRC program