European railway bridge stock consist mainly of 4 major bridge types, with age ranging form extremely old masonry arch bridges, middle-age metallic bridges and newly built concrete and composite (steel/concrete) bridges. Small span lengths, less than 10 m, are dominating. Furthermore railways typically assess serviceability as rout bases. Traffic interruptions need to be avoided almost entirely. Many of the existing bridges are in need prolonged life considering the design life when built. In addition it is not uncommon that the owner wishes to increase the speed, weight and traffic volume on the already busy routes. If these situations occur a thoroughly structural investigation is needed. First the remaining capacity is calculated, preferable with methods that consider real material data and loads. If uncertainties regarding for example boundary conditions exist monitoring might be needed. Nevertheless, if calculations and monitoring shows that the load carrying capacity is not enough strengthening can be one alternative to replace the structure. There are numerous different methods to strengthen existing structures of concrete, metal or masonry and the strengthen method chosen is largely dependent on the environment, type of original design, existing object, estimated future use and so on. In a sustainable society, the transportation work carried out by rail ought to be larger than today. In order to enable such an increase, the capacity of existing railway bridges needs to be increased too. This is also the objective of the project "Sustainable Bridges - Assessment for Future Traffic Demands and Longer Lives". There are three specific goals: 1. Increase the transport capacity of existing bridges by allowing higher axle loads (up to 33 tons) for freight traffic with moderate speeds or by allowing higher speeds (up to 350 km/hour) for passenger traffic with low axle loads. 2. Increase the residual service lives of existing bridges with up to 25%. 3. Enhance management, strengthening, and repair systems. A consortium consisting of 32 partners is carrying out fhe project. The gross budget is more than 10 million Euros. The partners represent the whole supply chain from user to producer/designer/ developer. This paper presents mainly the part considering repair and strengthening sys-tems for railway bridges. Many of the railways in use today were once built for completely other conditions than those we are facing today, especially when it comes to train speed, axis loads, and traffic intensity. Authorities, the Industry, and also the EU today require the train speeds and axis loads to be possible to increase. As a direct impact, existing railways must be assessed and possibly strengthened in order to meet the requirements on stability, settlements and induced vibrations. The following criteria's have been set up within WP6 - they follow mainly criteria's that have been set up by the Swedish railway authority Banverket. Strengthening works under traffic conditions must comply with regulations from the rail authority. Design of the strengthening should be carried out with reference to the function of the construction, e.g. to improve stability conditions, to reduce settlements or to reduce induced vibrations. Strengthening works should be possible to carry out under "on-going traffic conditions" with minimal impact on accessibility to the railway tracks and without, or with only marginal, reduction of train speed and axis loads. Strengthening should have minimal impact on the position of the railway tracks. Strengthening methods must be cost effective. Strengthening methods must be as harmless as possible to the environment. Strengthening works shall be carried out without damaging existing constructions, e.g. tracks, ties, ballast material, under ballast material, electric wires, signals, drainage equipments, etc. Each strengthening method must have a control program in which precautions, safety aspects, control measurements during installation, and verification after installation are covered. Strengthening should reduce the necessary amount of maintenance work during the life time of the construction, e.g. due to changes of the position of the railway tracks. If strengthening works should be carried out from the track (work within the track area), the following additional criteria apply: Installation should be carried out on railways closed for traffic and under limited time (may vary from authority to authority). Machines to be used must be adjusted to comply with "Free space along the railway line". Strengthening works must be possible to carry out without removing the existing tracks, ties, ballast material, electric wires, signals, drainage equipment, etc. In WP6 the strengthening methods studied has the above mention criteria's in common, even though in some cases deviations might exists. Work package 6 - "Repair and Strengthening of Railway Bridges", focus on a "toolbox" for Repair and Strengthening methods. WP6 consists of three main deliverables: "D6.1A guide for the use of repair and strengthening methods for railway bridges in Europe". In this deliverable a guide how to repair and strengthen existing railway bridges in Europe will be put together. Existing processes, systems and methods will be included in the guideline. In addition, also new developed method together with best practice methods will be addressed. Furthermore, emphasis is placed on workmanship and quality control during the repair and strengthening process. The second main deliverable is "D6.2 Research report regarding repair and strengthening of railway bridges in Europe". In this deliverable a summary of research and testing together with state of the art reports are conducted. The majority of the research is focused on new and innovative repair and strengthening methods. The last main deliverable is "D6.3 Field testing regarding strengthening of an existing railway bridge". Besides the results from the field tests, also a guides for implementation and assessment will be presented. In WP6 we are 13 partners from all over Europe; From Sweden; Luleå University of Technology, Sto Scandinavia, Chalmers University of Technology, Skanska Teknik AB, Swedish Geotechnical Institute (SGI) and Banverket. From Norway; Norut Teknologi AS, from United Kingdom; Salford University and City University, from Germany, Federal Institute for Materials Research and Testing (BAM) and Rheinisch Westfälische Tech. Hochschule (RWTH), Switzerland is represented by Swiss Federal Laboratories for Materials Testing and Research (EMPA) and finally from Denmark, COWI AS. All partners have different roles in the project and form sub-groups working together. In the coming sections are the content of the deliverables and consequently, work carried out in WP6 briefly described.