This master's thesis presents a methodology for maintaining concrete bridges, which involves several steps, starting from bridge monitoring, investigative work, and assessing the existing condition to developing technical solutions for bridge rehabilitation. The thesis is structured into two parts. The first part of the thesis focuses on studying the theoretical background related to bridge management, rehabilitation, and reconstruction. Emphasis is placed on the process of determining the most optimal bridge rehabilitation solution, starting from visual inspections, through investigative work, material testing, and finally, evaluating the existing condition of the bridge structure and the project itself. Additionally, a review of the most common rehabilitation measures for concrete bridges is provided. The second part of the thesis contains a solution for the rehabilitation and widening of a concrete bridge over the river Bednja in the village Ključ. This section includes a technical description, mechanical resistance and stability calculations, proof of the structure's load-bearing capacity, bridge layout, and the technical solution for rehabilitation drawings. The technical description covers the bridge rehabilitation solution, from preparatory work and reinforced concrete to drainage solutions on the bridge, all the way to finishing work. The structural analysis involves an examination of the relevant loads on the structure and a load-bearing capacity calculation.