In 2017, the canton of Geneva implemented Operation Papyrus, an innovative policy to regularize undocumented migrants. The Parchemins study was initiated in this context in order to measure the consequences of access to a residence permit on health, well-being and living conditions. Adopting an approach combining social determinants of health and life course, this interdisciplinary study collects quantitative and qualitative longitudinal data by following a cohort of people over several years. This publication reports on the results of the first wave of data collection. It describes the characteristics and motivations of undocumented economic migrants living and working in the canton of Geneva, their family and social situation, their housing and employment conditions, as well as their health status. These results fill a gap in the empirical data for this population in Switzerland and in Europe.