Defining and assessing sustainability of complex systems (ecosystems, production systems, territorial systems, etc.) is a crucial challenge for modern science. Several instruments are necessary to answer a lot of questions related to the interactions between man and Nature. Policy makers, businessmen, researchers, managers, environmentalists and common people need information in order to understand what is sustainability and what is the distance of their behaviours from it. Sustainability indicators have been developed with the purpose to answer all these questions.The paper presents the results of the SPIn-Eco project, a sustainability analysis of the Province of Siena (Italy). It has produced a data set that allows a practical comparison among several approaches and indicators by means of correlation analysis. Important correlations were found between Ecological Footprint and CO2 emissions as well as with the non renewable exogenous part of Emergy flow. No correlation was found between total emergy flow and total ecological footprin
