In this thesis, we review concepts in privacy and security for different classes of dynamical systems, with particular emphasis on opacity and attack detection. Opacity has attracted significant attention in recent years due to its role in tackling privacy-related problems within the area of system and control theory. Opacity is an information-flow property that is concerned with a system ability to hide information from an external observer. This property plays a key role in strengthening resilience against attacks and prevents adversaries from determining if their attacks have succeeded. We begin the thesis by examining opacity in its original setting of discrete event systems (DES) and consider a more recent adaptation for linear time-invariant (LTI) systems. In addition, we also provide some initial thoughts on how opacity might be formulated in the context of max-plus linear systems. Although maxplus systems constitute a subclass of DES, their formal structure resembles that of LTI systems. These models arise in practical setting such as manufacturing systems, communication networks, and railway systems, where synchronization and timing constraints are critical. To ensure the reliable operation of any system, it is essential to design mechanisms that mitigate the effects of malicious behaviour. This thesis also reviews concepts in security with a focus on attack detection, and discusses the connection between opacity and the notion of undetectable attacks.