# IoT-Enabled Smart Sustainable Cities: Challenges and Approaches
## 1 Introduction  
In between the urban context and Information Communication Technologies (ICT), the term _smart city_ is a relatively recent concept, whose diffusion has been rapidly increasing in the last years. Academic and industrial worlds, together with governments, institutions, and citizens, have coined several definitions for this emerging paradigm, which is now extremely popular and attractive. As an example, according to the authors of [1], a smart city could be defined as _\"a well-defined geographical area, in which high technologies, such as Information Communication Technologies (ICT), logistic, energy production, and so on, cooperate to create benefits for citizens in terms of well-being, inclusion and participation, environmental quality, intelligent development; it is governed by a well-defined pool of subjects, able to state the rules and policy for the city government and development.\"_More recently, together with first attempts of practical implementations, the smart city concept has been accused of being often too technology-centric, mainly driven by technological companies' own goals, while lacking real attention to the municipality and people's needs. Therefore, this has led to a generalized need for a more sustainable approach. Unlike the concept of smart city, _sustainability_ has a long history (being first introduced in 1987) and has been widely accepted. It is based on three main pillars or aspects: social sustainability, environmental sustainability, and economic sustainability [2]. A more recent definition [3] describes a \"sustainable city\" as an entity for which the inflow of material and energy resources and the disposal of wastes do not exceed the capacity of the city's surrounding environment. More practically, in order to achieve this goal, the consumption of urban resources in a city should match--or not exceed--the quantity provided by the natural environment (e.g., soil, water, or energy resources). Moreover, pollution levels resulting from the city's activities should not overwhelm the environment's ability to provide resources to citizens and other members of the ecosystem [4]. Even if extremely simple and logical, the sustainability concept has been criticized for being, in some cases, outdated and not suitable for the needs of the highly digitized current society, characterized by extremely rapid change and growth. As a consequence of these concepts' evolution, a new wave of academic discussions proposes a new paradigm, denoted as _smart sustainable city_, as a response to the current criticisms, proposing a more balanced approach. More in detail, this paradigm aims at combining urban sustainability and _smartness_ of a municipality, focusing on the fact that both aspects should simultaneously be considered to provide the best \"urban performance\". A comprehensive definition [5] describes smart sustainable cities as \"_innovative cities that use ICT and other means to improve quality of life, efficiency of urban operation and services, and competitiveness, while ensuring that they meet the needs of present and future generations with respect to economic, social, environmental, as well as cultural aspects._\"  
On the basis of these conceptual definitions, it is important to consider how a practical implementation of these concepts will affect the everyday lives of citizens. This is based on the new possibilities opened by the current wave of technological innovation and, more precisely, on the increasing adoption of devices and entities based on Internet of Things (IoT) technologies. The IoT paradigm is one of the key aspects guiding the technological evolution and involvements in several scenarios and contexts, through a multitude of connected devices operating and cooperating in order to sense the physical world and adapt their behavior taking into account the changing context of the environment where they \"live\".