The increasing attention to sustainability worldwide asks for sustainable practices in every sector. In this scenario, the construction sector has often been indicated as a leading protagonist of sustainable development. However, sustainable buildings are still rare and requests to push a sustainable transition of the construction sector are common. Meanwhile, studies and policies are discussing what a sustainable building is and how to measure sustainability in the built environment. The sustainability assessment of buildings has been diffusing thanks to the multicriteria rating systems. The paper discusses some limits of these systems. Then, it looks at trends in sustainability assessment. Given the integrity and complexity of sustainability in urban systems, assessments at larger scales are increasingly required. Sustainable neighbourhoods and cities are diffusing worldwide, whereas experiences of sustainability assessment at city level have started. These experiences show that the dynamism of cities prevent a static approach to the sustainability assessment and asks to consider new criteria in the sustainability assessment. The assessment has to become a path characterized by environmental, social and economic uncertainties. Finally, the paper shows by enlarging the scale of the assessment, it is possible to fully consider all the domains of sustainability, as the social and economic aspects.