This project will be the first comparative study to describe the basic properties of the sound systems, word formation processes and sentence structures of five major Iranian languages: Baluchi and Sorani (Northwest), Persian (Southwest), Ossetian (Northeast) and Pashto (Southeast). The comparative aspect of this project enriches our knowledge of a major language family. Data collection will be conducted via standard linguistic elicitation with native speaker consultants. The research team will transcribe, catalogue and enter the data into a database accessible to the public, and use the collected data to create content for Wikipedia pages. The results of this research will appear as journal articles and a book volume enumerating the grammatical similarities and differences of these languages, and thus opening up the opportunity for a broader description of them that will be useful to communities outside of linguistics. The theoretical goals of the investigation are to analyze some of the challenging grammatical properties of these languages: (1) examination of various types of ellipsis; (2) positioning of clitics, especially in those languages with split-ergative constructions, providing an ideal laboratory for investigating the interaction of syntax, morphology and phonology; (3) micro-parametric variation in passive constructions; and (4) the headedness parameter. The Iranian language family represents a cline of head-finality which bears on important theoretical hypotheses about the role of linearization algorithms and movement in determining word order. The theoretical aspect provides a crucial source of data for the development of theories of human language, and adds yet another layer to our linguistic knowledge. Finally, the micro-parametric comparison of these languages will break new ground in the evaluation of the existing linguistic theories regarding long-standing questions about parameters, whether they exist, and if so, where in the architecture of the grammar. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.