Immune-mediated diseases (IMDs) are increasing rapidly in the developed countries constituting a huge medical, economic and societal challenge. The reasons to this epidemic are not known, but exposome needs to play an important role since genetic factors cannot explain such a rapid change. In the HEDIMED project altogether 20 academic and industrial partners will join their multidisciplinary and supplementary forces to identify exposomic determinants which are driving this epidemic. The project is based on a combination of data and biological samples from large clinical cohorts constituting the largest clinical resource in this field including 350.000 pregnant women, 28.000 children prospectively followed from birth and 6.600 children from cross-sectional studies. HEDIMED focuses on common chronic IMDs that cause a significant disease burden, including type 1 diabetes, celiac disease, allergies and asthma. Exposomic disease determinants and the underlying biological pathways will be identified by exploratory approach using advanced omics and multiplex technologies combined with cutting–edge datamining technologies. Particular emphasis is paid on early fetal and childhood exposome since the disease process is known to start early. Inclusion of several IMDs makes it possible to identify determinants that are common for many IMDs facilitating the development of widely operating treatments. HEDIMED includes also data and samples from clinical trials that have used exposomice interventions and cell and organ culture models to help the identification of causal associations. HEDIMED will generate an open-access toolbox that offers various kind of data, new technologies, interactions forums, latest information and functional tools for several stakeholders to facilitate the efforts to find ways to control the IMD epidemic. HEDIMED will generate several innovations which can become exploited widely in diagnostic, therapeutic, preventive and health-economical applications. HEDIMED will work together with the other projects (EXPANSE, HEAP, ATHLETE, EQUAL-LIFE, LONGITOOLS, EPHOR, REMEDIA and EXIMIOUS) funded within the Human Exposome programme call H2020 SC1-BHC-2018-2020, in order to achieve collaboration and synergy