To understand brain function, we need to understand brain structure. The evolution of mammals has led to many differences in brain anatomy, but we know very little how those differences correlate to the wide diversity of animal behavior. This collaborative project is to consolidate and make more accessible for research and education two major collections that form a unique, extensive, remarkably preserved assembly of comparative mammalian brain specimens. Together they contain more than 275 sectioned and stained brains, including over a half million microscope slides, representing over 150 species, from 50 Families in 17 different Orders of Mammalia. Many specimens are irreplaceable, from rare or endangered species, and so can provide critically unique data for questions about biodiversity. The collections are being brought to a national museum facility in Washington DC to join complementary extensive human brain collections, and so establish a single site for storage, curation, and research on comparative mammalian brain neuroanatomy. An electronic/website also is being developed, including several selected images, which researchers could access worldwide for data, or use to evaluate whether to make a research visit to the site itself to examine the original material. The impact of this project is high. First, it safely preserves for future research an irreplaceable resource that also represents a scientific investment of more than 50 years of exacting work by dozens of people. Second, it promotes multidisciplinary research on comparative neuroscience, behavior, and systematics to understand the diversity in the most complex organ known, adding computational expertise for technological development of digital imaging and multidimensional databases. Third, it provides a working base as well as a model for sharing complex morphological data with other collections, such as those on non-mammalian vertebrate brains. Fourth, the project will have educati onal as well as research impact by providing easy website access to information about the vertebrate brain in the context of biodiversity.