To better understand the identities and roles of brain cells, NIH’s Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative launched an international network of collaborating researchers called the BRAIN Initiative Cell Census Network. Its aim is to create a comprehensive inventory of all the cells in the human, nonhuman primate, and mouse brains, including cell locations, interconnections, and activities. The study of brain cells across species can pinpoint features that are uniquely human and give insights into which animals to study for different scientific questions. The latest findings were reported in a series of more than 20 papers published in Science, Science Advances, and Science Translational Medicine on October 13, 2023.