The circular economy implies new challenges and targets to mitigate the impact of new production cycles by using post-production processes, such as the reuse and repurposing of components in the case of steel, whose high potential is already acknowledged for recycling. The PRIN 2022 research project, titled “Buildings and Circular Economy - Steel from Production to Post-Production - Law and Responsibility Issues” focuses on this operational scenario. The research project aims to define methods and tools for reusing metal components resulting from buildings decommissioning, and, in the case of designing new structures, strategies for an efficient design that integrates both disassembling and reassembling construction elements. The first results of the research project are summarized in this contribution, which aims to reconstruct the regulatory framework at both the national and European levels, related to the practice of reuse and, in particular, to the application of CE marking. This process can play a crucial role in the start of a new phase of the circular economy, pushing the reuse of steel products for the reduction of environmental impacts and the development of a new and promising economic model.