Patient registries that document real-world clinical experience play an important role in cardiology as they complement the data from randomized controlled trials, provide valuable information on drug use and clinical outcomes, and evaluate to what extent guidelines are followed in practice. The Platelet Inhibition Registry in ACS EvalUation Study (PIRAEUS) project is an initiative of registry holders who are managing national or international registries observing patients with acute coronary syndromes (ACS). The aim of PIRAEUS is to systematically compare and combine available information/insights from various European ACS registries with a focus on P2Y12 inhibitors. The present publication introduces the 17 participating registries in a narrative and tabular form, and describes which ACS groups and which dual antiplatelet therapies were investigated. It sets the basis for upcoming publications that will focus on effectiveness and safety of the antiplatelets used.