The selection of indicators for the Observatory of Sustainability of the Algarve Region for Tourism (OBSERVE), poses challenges, namely which indicators are relevant to stakeholders and how to assure that information is available. To support the selection of the environmental, sociocultural, economic and institutional indicators, an engagement process was designed and applied, which included meetings with stakeholders, a workshop and an online survey. The results showed that both workshop and online surveys reflected, in general, similar opinions, thus allowing the selecting of the sustainable development indicators for the Algarve region. Additionally, the results showed that nearly 75% of the indicators can be obtained from national statistics and, therefore, can be used on the OBSERVE project, assuring a quick flow of information. As limitations, it is important to mention that the other 25% will need further development, in order to provide data for indicators, like carbon management and client satisfaction. With this approach, the observatory will survey and evaluate the sustainable development of the region (status and trends), based on indicators that answer to the strategic needs of system's main users, with social and economic implications, i.e., public institutions, economic agents, tourists, local communities and residents.Sustainability 2019, 11, 444 2 of 24 of the overnights of 34%, corresponding to the most important touristic region in Portugal. In a 10-year strategy [4], sustainability is one of the 10 challenges proposed by the Portuguese tourism policy (2017).Monitoring is essential for considering and identifying the trends, dynamics that support policies, strategies and stakeholders decisions using different type of information, from adequate statistics [5] to other database sources, such as TripAdvisor [6].Observatories have an important role in monitoring and supporting decisions at public and private level, showing the status and trends of the sustainability development reality. The OBSERVE project-Observatory of Sustainability of the Algarve Region for Tourism [7], under development by the University of Algarve, intends to be an instrument for monitoring and evaluating the sustainability levels of the region. Its main goal is to provide environmental, economic, sociocultural and institutional indicators to support the decision-making process, for a sustainable growth of the Algarve region. This two-year project seeks the widest possible participation from central and local administration, universities and research centres, as well as, enterprises, associations, tourists and citizens, aiming to be an added value for the stakeholders.The Observatory should reflect the region's performance, responding to the strategic needs and expectations of the different stakeholders, as well as assuring that information is uploaded automatically from reliable and updated sources, in order to ensure the continuity of the OBSERVE platform in the future [8].The selection of the indicators is considered a fun...