Milk—it’s what distinguishes mammals from the rest of the animal kingdom. It’s also an incredibly complex substance, and scientists are still working to identify the many chemical components of milk and the roles they play in nutrition, immunity, brain development and other areas. As part of this effort, researchers at the National Institute of Standards and Technology (NIST) and the Smithsonian’s National Zoo and Conservation Biology Institute are studying the unique milks of many species. In a related project, NIST scientists are also studying the composition of human milk. This research will help zoos raise healthy animals and help scientists understand how mother’s milk promotes the development of healthy human babies.