This paper discusses the factors to be considered when repairing reinforced concrete structures where the reinforcing is corroded, and the response of the structure under repair to the changes exerted by the repair to the overall system durability. Failure to recognize the system concept in repair projects and to properly define the system and its associated interactions with the environment have led to many notable repair failures. Critical issues of a durable repair system such as volume changes, tensile strain capacity, compatibility of repair materials, design and finally work-manship are discussed briefly.