DRD4 counts 67 research institutes and seven (semi-)industrial partners, listed in Annex A and B of the Proposal document. The status of the industrial partners is somewhat restricted compared to ”normal” groups from universities or research labs. The main purpose for this distinction is the avoidance of conflicts of interests (see Annex B).
Most participating groups have a high energy physics background with experience in photodetection and particle identification from ongoing experiments including ALICE, BELLE II, COMPASS, DUNE, EIC, LHCb and their planned upgrades. There are also groups that work on future studies including particle ID at a future electroweak and Higgs factory (e.g. FCC-ee).

The DRD4 collaboration has a dual structure reflecting the broad range of ambitions and goals of the participating members. As shown in the organigram (see Fig. 1) DRD4 comprises six Working Groups (WG), WG4.1 - WG4.6, and a number of five Work Packages (WP) following the themes (DRDT) defined by the ECFA Roadmap process. WPs are currently numbered from 4.1. to 4.5. Each WP comprises typically a few tasks numbered from e.g. 4.1.1 to 4.1.3. All items numbered in DRD4, incl. milestones and deliverables, begin with ’4.’ to distinguish them from other DRD collaborations.