The mission of the Mouse Mutant Resource (MMR) at The Jackson Laboratory (JAX) is to provide mouse models for biomedical and biological research. Spontaneous mutations continue to be a major source of mouse models for human disorders. They complement specifically targeted mutations and have the advantage that they are first recognized by biomedically-relevant phenotypes and do not require prior knowledge of the underlying genes. The specific objectives of the MMR program are to 1) identify the causative genetic mutation in spontaneous mutant strains with heritable phenotypes using SNP-based mapping and high throughput sequencing (HTPS); 2) characterize new mutants phenotypically by defining their anatomical, histopathological, physiological, and ultrastructural abnormalities; 3) provide resources to the scientific community by publishing information on new mutants, preserving them as frozen gametes or embryos and DNA for future molecular analysis, and distributing mice to other investigators, and 4) enhance the identification rate of causative mutations using comparative genome hybridization, RNASeq and improved bioinformatics analysis methods for HTPS. New mutants are discovered as pljienotypic deviants appearing in JAX's large breeding colonies and characterized genetically by determining mode of inheritance, testing for allelism with known mutations that produce similar phenotypes, determining chromosomal locations and identifying the mutated gene using exome or whole genome sequencing. Each new mutant is characterized phenotypically by observing its growth, viability, fertility, life span and behavior and by defining its anatomical, histopathological and physiological abnormalities. For those mutants with phenotypes that model human disorders, deeper phenotyping is carried out to enhance their value. The MMR team has expertise in bone biology, reproduction, general histopathology and neuropathology; we collaborate with experienced investigators in other fields including hearing, vision and metabolomics. All new mutants are published in peer-reviewed journals or presented on the MMR and JAX web sites, and related information is made available through the Mouse Genome Database.