This issue of the Network Industries Quarterly looks into the regulatory challenges facing the development of smart cities. With the acceleration of technological developments in network industries and, in particular, in infrastructures, there is a constant need to review regulatory schema. Demographic changes, climate change, and the evolution of Information and Communication Technologies (ICTs) are disrupting the traditional landscape of urban infrastructure services and questions are arising. How should the sharing economy be regulated in order for regulators to invest in the infrastructure that supports it? How should public goods and services including transportation, telecommunications, water and energy be managed and distributed? While the possibilities are exciting and innovation continues to gain momentum at an accelerated pace, challenges are inevitable especially when it comes to infrastructure financing and the general management of smart cities. Following the 6th Conference on the Regulation of Infrastructures which took place on 16 June 2017 with a particular focus on the regulatory challenges facing smart cities in the transport, telecoms, water and energy sectors, four papers were selected for this publication due to their topical relevance. Olivera Cruz and Miranda Sarmento address the regulation and financing of smart cities through Public Private Partnerships (PPPs), and how that financing can be put to use to make infrastructure smarter as quickly as possible through an in-depth analysis of the various PPP models used to date, and possible improvements. Bock and Hosse present a digital model in development for the planning, tracking and analysis of passively generated mobility data for regulators. The model aims to facilitate the use of intelligently managed renewables by providing easy alternatives for the car to transport users. Marlot and Brunel look at Mobility as a Service (MaaS) and how regulation can incentivise consumers to choose shared mobility over the private car. Finally, Knieps provides an overview of the network economics of smart, sustainable cities, with a focus on the potentials for sharing activities and prosumage, as well as smart congestion management.