This is the DEU-IV dataset, the latest iteration of the Decision-making in the European Union project. While previous versions focused on the Council of the EU, DEU-IV systematically applies the framework to the European Parliament (EP) for the 2019–2024 term. The dataset employs the spatial model of politics to map the latent preferences of party groups, the Commission, and the Council across 113 controversial policy issues. The dataset is constructed using triangulated semi-structured interviews with 119 policy experts, supplemented by document coding and amendment analysis. By capturing the pre-negotiation ideal points and the final legislative outcomes, DEU-IV reveals the internal mechanics of supranational bargaining and the influence of legislative committees