The book explores, through new studies, the theme of security in its multiple dec-linations from a comparative and European public law perspective. It highlights the current complexity of the dynamics related to public security at the domestic and international levels and the reflections that these dynamics may have on contemporary constitutionalism and the rule of law. It critically examines how contemporary challenges reshape the concept of security and its relationship with democratic governance and fundamental rights. From this perspective, the volume presents different analytical contributions that together create a multifaceted picture, as does the importance of new reflections on emerging challenges, such as those deter-mined by evolving technologies. In light of this picture, by integrating theoretical analysis with empirical case studies, this volume provides a comprehensive per-spective on security and defence governance in contemporary legal systems and helps to understand the complexity of security profiles, which today tend to intertwine. These analyses increasingly demonstrate the need for state resilience, re-sponsiveness, and the coordination of public defence and security policies.