Over the past few decades, it has become increasingly obvious that almost half of the languages spoken around the world are threatened with extinction. As linguistic diversity is essential to human existence, researchers started focusing on language documentation, maintenance and revitalization, raising awareness of the need to safeguard the linguistic heritage, and creating red books and databases of endangered languages. However, when it comes to Serbia, these databases differ widely in terms of assessing language endangerment, and often give insufficient or inaccurate data on the varieties spoken here, also lacking to provide empirical support for their assessment. Our Project’s ambition is to create a precise tool for assessing the degree of language endangerment and vulnerability, and to apply it to a statistically significant sample of speakers in Serbia. The tool will be applied to the following linguistic varieties, carefully chosen based on the international assessment and our own field research: Aromanian, Banat Bulgarian, Vojvodina Rusyn (Ruthenian), Judezmo (Ladino), Romani (Gurbet and Arli varieties), Megleno-Romanian and Romanian (Bayash and Vlach varieties). The result will be an accurate assessment of the degree of vulnerability of the languages and linguistic varieties spoken on the territory of Serbia, which could be used as a solid reference in the future for any sociolinguistic research. The absolute novelty of the research proposal is that, in parallel with the application of the carefully conceived sociolinguistic questionnaire, meant to assess factors influencing language vitality, it will also document and archive speech samples of vulnerable linguistic varieties, over three generations of speakers. Based on the collected data, a database, a graded scale of vitality and an interactive map will be created that would provide insight into the vulnerability of specific varieties in the studied communities. Furthermore, it will help build support for language communities, NGOs and the government in their efforts to maintain and revitalize these languages. Finally, the tool for assessing linguistic vulnerability, which is the result of the Project, may serve as a reliable instrument in other language communities worldwide.