Language loss is one of the most urgent problems facing linguistics, posing scientific, practical, and moral challenges of enormous proportions. Thus it is remarkable that no centralized, up-to-date source of information on the world's endangered languages currently exists. Although there are many sources with partial coverage, none provides all the information needed to support documentation, analysis, education, and revitalization efforts. <br/><br/>The Endangered Languages Catalog project (ELCat) is designed to provide accurate, up-to-date information on the endangered languages of the world, i.e., a definitive catalog of languages at risk. It will correct errors in existing databases and provide new data not available from existing sources, offering this information in an accessible, updatable online format. <br/><br/>The catalog will allow users to assess, not only how critically endangered a language is, but also how much it can contribute to scientific knowledge and how well it has already been described. Thus it will provide information on: (1) the number, age, and location of the speakers, (2) the genetic affiliation of the language, and (3) what descriptive materials and projects already exist. The content of the catalog will be developed by the linguistic research teams at the University of Hawaii and Eastern Michigan University, in collaboration with regional experts. It will be designed so that scholars, community members, and other users can submit and annotate catalog information in many different ways, e.g., via smart phone, as well as conventional Internet applications. <br/><br/>The ELCat website will be a means of raising public awareness and fostering increased research on endangered languages. It will also constitute a resource for communities whose languages are at risk, providing them with materials to support language preservation and revitalization activities. At the same time, ELCat will contribute to advances in the social and human sciences. The most pressing research priority in linguistics and other cognitive sciences is the documentation of those endangered languages whose disappearance would mean loss of knowledge of the full range of linguistic diversity. By providing information on these languages, ELCat will not only expand scientific knowledge of human language but also further understanding of human cultures and cognitive abilities.