Thirty two people participated in the 4th POSEIDON General Assembly, that took place in the University of Coimbra, Portugal, on 10-11 July 2019. The meeting was opened by POSEIDON’s Project Coordinator and Technical Leader, Mr. Francesco Paolo Schiavo (MEF) and Mr. Dario Beltrame (ACN). POSEIDON is now at a critical point of its workplan, with the development of interim implementations of its main building blocks, namely, Blockchain, Web Dashboard, Risk Management Module, and Personal Data Analyser, and the planning of the various pilots. In addition to presentations and discussion, the General Assembly provided an opportunity for parallel hands-on sessions, addressing the overall integrated architecture, the staging environment, flow and functionalities of the implemented blockchain core mechanisms, data management flows, APIs verification, and integration strategy and services. An assessment of the main implemented platform components and validation was done, in order to enable pilots implementation and use-case deployment phases by the involved partners. There was also a session with a representative of the PAPAYA project, for discussing possible collaboration between the two projects, namely in what concerns the use of the Web Dashboard. Last but not least, dissemination activities, exploitation of results and market analysis were also subject to discussion and analysis.