In cybersecurity, mastering fundamental concepts is crucial for both new and seasoned professionals. This chapter provides an in-depth exploration of the core principles that underpin cybersecurity practices. We begin with the CIA Triad—Confidentiality, Integrity, and Availability—examining its components and practical applications. We will then move into key security models and frameworks that shape the creation of security policies, followed by an analysis of different types of security controls. The chapter will also highlight the importance of risk management and threat identification in securing systems. Finally, we will discuss Defense in Depth and Security Architecture as vital approaches to building robust and resilient security environments.