ARGO is an international global ocean observing system based on an array of some 3.000 autonomous floats drifting freely in the world’s oceans. Those floats, which probe the water to a depth of 2.000 m and report temperature and salinity data to land stations, constitute one of the essential components of the Global Climate Observing System. They also provide invaluable data in support of ocean and climate research, operational oceanography and ocean monitoring. The system is implemented by a large number of agencies and scientists in over 40 countries. A high level of coordination is necessary to organize efficiently the operations at sea, maintain the array, and to perform the required tasks of data management (e.g. collection, validation and quality control, distribution and availability, and safe keeping). The main objective of the EURO-ARGO consortium is to organize and consolidate the European contribution and to set up a research infrastructure in support of the global ARGO programme. Euro- ARGO having been endorsed by the ESFRI (European Strategic Forum on Research Infrastructures), the Preparatory Phase Project had several objectives to progress towards defining the appropriate legal framework, and to address several critical technical points related to instrumentation and sensors, data management, and array design. Capacity building and outreach have also been given due consideration. The most important results of the project can be summarized as follows: After extensive review of possible legal frameworks for the EURO-ARGO RI, it has been decided to adopt the ERIC status. Since this is a new concept (which was elaborated by the Commission during the course of the project) it has taken some time to obtain agreement by the project participants to join in the Consortium. The EURO- ARGO ERIC statutes have been drafted, including the governance structure, which consists of a Council, a Management Board, a Programme Office and a Scientific and Technical Advisory Group. The EURO- ARGO ERIC will include members and observers. Budgets have been proposed for the first five years, with an examination of the anticipated expenses and possible sources of national and international funding. It has been agreed that the research infrastructure will be distributed, with national activity centres and the Central research infrastructure (the ERIC) to be established in France at Ifremer. As of the end of the project, France, Germany, United Kingdom, Italy, Spain, Netherlands, Bulgaria and Greece will be members, and Ireland, Poland, Portugal will be observers. The draft statutes have been endorsed by the French ministries and forwarded to the Commission for review. The technical activities of the project considered the status of float technology and its likely evolution over the coming years (design, lifetime, cost, new sensors, improved telecommunications, etc...). A comparative evaluation has been made of new sensors like O2 and bio-geochemical sensors, ice sensing algorithms, vertical sampling strategy, transmission systems (Argos and Iridium), batteries etc. A comparison of the performances of different types of floats (Provor, Nemo and Apex) has also been made. Sampling strategies for the Nordic, Mediterranean, and Black seas have been examined. Four aspects of data processing and distribution system have been considered: enhancement of the mandatory functions related to ARGO Regional centres both in Nordic seas and in Mediterranean and Black seas; the development of new tools to help float deployment plans and monitor the behaviour at sea; definition of real-time quality control procedures for biochemical data; and improvements of the consistency of the ARGO dataset. Finally, a European ARGO user group has been set-up, outreach activities have been carried out in the Black sea; an educational web-site has been posted with pedagogical and illustrative material on ocean dynamics, observations, and the ARGO system.