This textbook provides an overview of the topics related to IT security. The digital transformation opens up many new opportunities, which can radically change business models and administrative processes. However, as digitalization progresses, the complexity of IT systems and infrastructures increases. Additionally, the methods of professional attackers become more sophisticated, and the targets of attacks continuously become more lucrative, leading to significant damage for companies and society as a whole. Therefore, it is crucial for the successful future of our society to counteract these increased risks and to create a secure and trustworthy IT environment. It is necessary that new developments and processes in cyber security accompany the growing challenges. You can read about these advancements in the second edition of the textbook "Cyber Security" by Prof. Norbert Pohlmann. In the revision of the very successful first edition, existing chapters have been supplemented and updated, and new chapters have been added for new topics. Teaching materials, including 19 complete lectures and exercises, have also been adjusted and expanded. Over a total of 746 pages, computer science professor Norbert Pohlmann provides fundamental knowledge about cyber security and delves deeply into innovative topics such as Self Sovereign Identity and the Trustworthiness Model. The author emphasizes the importance of not only conveying theoretical expertise but also enabling the reader to view cyber security from a practical perspective. With the help of this textbook, you will learn more about the mechanisms, principles, concepts, and characteristics of cyber security systems, allowing you to assess the security and trustworthiness of IT solutions. Fundamental aspects of cyber security.