This book covers the topics on cyber security in IoT systems used in different verticals such as agriculture, health, homes, transportation within the context of smart cities. The authors provide an analysis of the importance of developing smart cities by incorporating technologies such as IoT to achieve the sustainable development goals (SDGs) within the agenda 2030. Furthermore, it includes an analysis of the cyber security challenges generated by IoT systems due to factors such as heterogeneity, lack of security in design and few hardware resources in these systems, and how they should be addressed from a risk analysis approach, evaluating the risk analysis methodologies widely used in traditional IT systems.