While today’s galloping urbanization weighs heavily on both People and Environment, the massive instrumentation of urban spaces appears a landmark toward sustainability. Because of their high sensitivity, the wide range of their observables, their energetic self-sufficiency and their low cost, nanosensors appear particularly well suited to urban metrology. A 8 years, 9 M¤ equipment project funded by the French ‘Programme d’Investissement d’Avenir’ starting in 2012, Sense-City project offers high-quality facilities for prototyping and performance assessment of urban nanosensors. Sense-City is built around four programs, environmental monitoring, structural health monitoring, energy performances monitoring and people exposure monitoring. We present the activities of the consortium partners along these lines, the complementarity of our skills enabling the design of decision-support tools based on innovative sensors, precise modeling as well as data management and visualization. We also discuss the shortcomings of evaluating the performances of sensors only in lab conditions or directly in real, urban conditions. As a solution, Sense-City will provide an environment of intermediate complexity for the testing of environmental sensors, a realistic urban test space in climatic conditions, both far more complex than clean rooms and far more controllable than actual cities.