Following the ICOMOS study “The World Heritage list: filling the gaps – an action plan for the future” and the Global Strategy of the UNESCO World Heritage Committee (WHC) encouraging State Parties to submit nominations on the 20th century Heritage, ICOMOS-Portugal presented an Ensemble of works of Álvaro Siza for the World Heritage (WH) Tentative List, in 2017.  Siza is not only an Architect of national relevance, but also international; as one can count the design of approximately 500 projects and built works (spread across 4 continents and 16 countries), more than 100 distinctions and awards, 19 PhDs Honorary degrees, hundreds of dedicated publications. Despite the international recognition of the quality of Siza’s architecture, there is not yet a complete and systematic inventory of his built works. The information is usually scattered, partial or incomplete. The existent literature focuses more on formal questions of the project, and little on the constructive and technical dimension of his works, on the state of conservation of the buildings, or on possible threats affecting them. In this framework, the scope of SizaATLAS project is to address a comprehensive inventory of all of Siza’s built works, and to develop a detailed documentation and analysis of the 18 buildings selected for the WH List. This research and the comparison with other contemporary architecture will result in a better understanding of the unique value of Siza’s architecture, in a national and international context. This will be key to establish the justification of the Oustanding Universal Value (OUV) of his work, its national protection and an effective management system to support the instruction of Siza’s works nomination for the WH List. The research intends to develop: 1) a COLLABORATIVE PLATFORM for open access, which will allow database management and exchange, as well as forms' compilation and research dissemination; 2) a georeferenced INVENTORY of all the built works by Siza, ...