The marmoset, a type of small monkey native to South America, is a research model of increasing importance for biomedical research in the United States and globally. Marmosets offer a range of advantages as animal models in neuroscience, aging, infectious diseases, and other fields of study. They may be particularly useful for the development of new disease models using genetic engineering and assisted reproductive technologies. However, concerns have been voiced with respect to the development of new marmoset-based models of disease, ethical considerations for their use, the supply of marmosets available for research, and gaps in guidance for their care and management. To explore and address these concerns, the Roundtable on Science and Welfare in Laboratory Animal Use hosted a public workshop on October 22-23, 2018, in Washington, DC. The workshop focused on the availability of marmosets in the United States and abroad; animal welfare and ethical considerations stemming from the use of wildtype and genetically modified marmosets; and standards of housing and care, dietary needs, and feeding requirements for marmosets in captivity. This publication summarizes the presentations and discussions from the workshop.Table of ContentsFront Matter1 Introduction2 Context for the Use of Marmosets as Animal Models3 Ethical Considerations4 Current Research Applications5 Marmoset Genomics and Genetic Diversity6 Marmoset Supply and Availability7 Marmoset Care and Management8 Final RemarksAppendix A: Workshop AgendaAppendix B: Professional Biosketches