The Underground Artworks in the Frame of the New Projects for the Rehabilitation of the Romanian Railway Network Summary With the aim to upgrade its railway network developing it in compliance with the modern European technical standards, the Romanian Government assigned to the Joint Venture Italferr, Obermeyer, Tecnic e Scott & Wilson the task for the technical assistance having as subject the updating toward the European standard and the target to get the complete interoperability for the railway lines relevant to the entire Corridor IV inside the Romanian country. With reference to the two sections Predeal-Brasov (26 km) and Craiova-Calafat (107 km) the abovementioned JV carried out only the Feasibility Studies while, on the contrary, for the three main sections Brasov-Sighisoara (130 km), Sighisoara-Coslariu (98 km) and Coslariu-Simeria (68 km) the subject of the Technical Assistance has included all the design phases starting with the Feasibility Studies and then following with the Technical Design and finally with the Detailed Design. In the frame of the subject it has been included too the preparation of the technical specifications and the supervision of the geotechnical investigation carried out along the entire path having length of 429 Km covering all the five abovementioned railway sections. With reference to the Predeal-Brasov section the studies carried out have suggested an alternative with only one double pipe tunnel having the not usual length of 22.485 m. The most important infrastructures designed for the entire section from Brasov to Simeria are consisting in six viaducts for a total length of 6 km and in eight tunnels for a total length of 15 km. The two longest tunnels, having length 5,5 Km and 6,8 Km, have been designed in order to be excavated by TBM under high overburden. All the tunnels have been designed in strictly accordance with the TSI (Technical Specification of interoperability relating to safety in railway tunnels in the trans-European conventional and high-speed rail system”) 2008/163/CE. In the frame of the Technical Assistance Contract Italferr S.p.A., the Engineering Company fully owned by Ferrovie dello Stato S.p.A., assured the co-ordination of all the services carried out by the partners and by the subcontractors, while Italferr S.p.A has directly designed all the underground artworks and all the railway signaling technologies including too the ERTMS 2nd level and the relevant new GSM-R network. The present article has as subject the description of the main technical characteristics of the railway sections whose upgrading has constituted the subject of the abovementioned Technical Assistance with special reference and focus on the underground artworks.