The development of fast breeder reactor (FBR) design codes in Europe has been determined by the way in which the FBR itself has developed. Until 4 yr ago, there were four main streams of development, each largely independent, but with a small amount of international participation. In parallel with the independent development of reactor systems in Europe, different approaches to design codes have emerged. Until the Superphénix project, there was a deliberate attempt to avoid developing any formal code before proceeding with design and construction. France is the only European country to have published a complete code concerning FBR components: RCC-MR (Regies de Construction et de Conception des Matériels mécaniques des Réacteurs rapides—Design and Construction Rules for Mechanical Equipment in Fast Breeder Reactors). In 1984, five European governments (Belgium, France, Italy, the United Kingdom, and the Federal Republic of Germany) agreed to a coordinated program for FBR research, development, and construction. The ultimate outcome must be a common design code. Drawing up such a design code represents a major challenge in the field of international collaboration. It seems likely that the existing RCC-MR code will be used as the starting point for the development of European design rules. Recently, European manufacturers set up a committee with the object of amending and supplementing RCC-MR.