Annex 91 is a collaborative project aimed at improving the energy performance of buildings through Building Information Modeling (BIM). By focusing on the Open BIM methodology and considering the Industry Foundation Classes (IFC) standard, the project seeks to create an integrated environment for data interoperability throughout the stages of building development and operation. The main objectives include integrating energy efficiency into BIM processes, empowering small and medium-sized enterprises, and advancing national and international interoperability. Deliverables include the development of a common BIM library, identification of use cases, creation of ontologies, testing and validation, formulation of modeling guidelines, and case studies. By fostering collaboration among experts from various fields, the initiative aims to enhance the design, construction, and operation of buildings to promote sustainability and resource optimization.