The fast growing ofIntelligent Internet of Things (IoT) Internet of ThingsInternet of Things (IoT) (IoT) has made heterogeneous smart devices able to connect seamlessly with each other with billions of such devices, and it is changing conventional cyber–physical systems in healthcare, smart cities, transportation, manufacturing, and agriculture sectors. Nevertheless, the massive incorporation of resource-constrained devices, distributed architectures, and open communication channels present serious issues associated with processing of data, securitySecurity concerns, and maintaining privacyPrivacy. To avoid such concerns, new developments combine Artificial Intelligence (AI) and Machine Learning (ML) into IoT ecosystems, giving way to Intelligent IoTIntelligent Internet of Things (IoT) (IIoT) systems which can automatically learn, and make decisions in real time and perform analytical functions. Nevertheless, IoT environments are strongly vulnerable to the cyber threats such as malware injection, unauthorized access, denial-of-service attacks, and manipulations of the anomalies, which require vigorous and dynamic securitySecurity systems. This chapter includes the overview of intelligent and secure IoT systems, emphasizing the AI-based predictive securitySecurity models, threat detection techniques, and privacyPrivacy-compatible data processing approaches. The chapter further elaborates architectural requirements, challenges, and research opportunities on the construction of efficient, resilient, and trustworthy self-defensive IoT systems. The findings clearly indicate that intelligent securitySecurity mechanisms constitute a fundamental prerequisite for achieving reliability, dependability, and secure large-scale deployment of IoT technologies in critical real-world applications.