In smart cities, technologies and systems of various types, from manual sensors to data collection devices, cooperate to improve citizens' wellbeing. They take advantage of information technologies and the internet of things (IoT) to increase citizens' welfare through the implementation of services with distinct objectives, like reducing energy consumption and improving transport routes and health services. Due to their functionalities and characteristics, IoT devices work interconnectedly and collect large amounts of data. In this context, cybersecurity and privacy arise as topics of central interest, as security breaches can lead to personal data exposure and service interruptions and malfunctions, thus directly affecting citizens' welfare and the implementation of the Sustainable Development Goals. This chapter discusses how cybersecurity risks affect smart cities' operations and citizens' welfare. It presents some current cybersecurity techniques and how to apply them in the smart city context. It also reviews some open issues and future directions.