Abstract The need to define sustainability and identify meaning and scientific foundations of the concept has been compelling during the last decades. Systems approach has been largely contributing to describe the reality in which we live and understand how to measure the progress of human action towards sustainable development. Professor Sven Erik Jorgensen directly and indirectly stimulated scientific advancements in the field of sustainability definition and evaluation. His work, especially focussing on the wide view of systems sciences, of which he has always been one leading promoter, was also interestingly devoted to study the relationships between human behaviour, society, policy, education and the environment at the global level. Inspired by this view, we present and discuss a list of aspects that can be crucial in the attempt of evaluating the sustainability/unsustainability of our development models, and reflecting the multidimensional and interconnected nature of the concept. In particular, we focus on the global dimension of sustainability; the need of holistic approach, that considers relations within and among different systems at different scales; the use of intensive and/or extensive indicators for investigating sustainability; and, in more practical terms, the need of data and knowledge to feed evaluation tools. The focus on these needs will contribute to a better understanding and diffusion of the concept of sustainability under a systems perspective.