Rational: Despite the development of unofficialy occupied living-places ("squats") in France and Europe, there is a lack of scientific data concerning these invisible living situations and precarious housing conditions that are difficult to reach. Hypotheses: People living in unofficialy occupied places in the city of Marseille are numerous and heterogeneous, combining complex life and health histories with precarious and risky living conditions. Objectives: This project is co-constructed by associations and community organizations, involved people, public authorities and scientific laboratorie. It aims to estimate the population of people living in squats in the city and to describe their pathways. The main objective is to understand their living conditions, to identify barriers and levers to access to essential social and health services, and to characterize existing resources and empowerment strategies. Methodology: The project will use a mixed, participatory and community-based methodology with: 1) a quantitative part using Respondent Driven Sampling (RDS) and a questionnaire survey (n=400) associated with the capture/recapture method and; 2) a qualitative part based on semi-structured interviews (n=30), focus groups and observations with the use of mind mapping. Expected results: This cross-analysis of statistical and empirical data aims to improve understanding of the situations of people living in squats, and to propose targeted actions to reduce risks and vulnerabilities and empower residents. The results of the triangulation and integration of quantitative and qualitative data will be discussed with all project partners, and will be the subject of scientific publications and presentations to the different stakeholders - institutional, community, associative and academic. This interdisciplinary and intersectoral (science-society) project is in line with the major priority issues of INSERM (Public Health), CNRS (Health and Environment) and INSHS (Shared Sciences and Experimental Approaches in SHS).