This work, fruit of the research activities of the Centre of Excellence on sustainable finance for infrastructure and smart cities (ExSUF), set up in 2021 from the «Committee on Housing and Land Management» of the United Nations Economic Commission for Europe (UNECE) and from LIUC - Cattaneo University, aims to describe the state of the art in the regulations and principle features and definitions of sustainable finance and smart cities, analyzing the classical schemes of project financing and PPPs and highlighting the present scenario in which public and private actors, and, in particular, private capital entities move. By means of a market analysis of PPPs in Italy and thanks to requests coming from discussions with practitioners and sector experts, the text concludes by showing how classical PPPs models have to evolve to guarantee flexibility and to promote constructive dialogue between public entities and the private sector with the goal of identifying new financial and design metrics and new ways of putting them into practice.