An Introduction to Holography

This article provides a pedagogical review of the AdS/CFT correspondence and the broader field of holography. It is aimed at graduate students with a background in general relativity and quantum field theory who are beginning to study holographic dualities and quantum gravity. The text develops the subject from its conceptual foundations, beginning with black hole thermodynamics and the holographic principle, before introducing conformal field theory, Anti-de Sitter geometry, and the basic structure of the AdS/CFT correspondence. Particular emphasis is placed on developing physical intuition and on explaining how spacetime geometry, quantum information, and quantum field theory become interconnected within holography. The review then introduces bulk reconstruction, subregion duality, entanglement wedge reconstruction, and the role of quantum error correction in the emergence of bulk spacetime. Finally, it discusses the challenges of extending holography beyond Anti-de Sitter space, with an introduction to de Sitter holography, observer dependence, and the broader perspective that spacetime geometry and gravitational dynamics may emerge from more fundamental quantum-information-theoretic structures. While the presentation remains largely conceptual and pedagogical, selected derivations and technical details are included throughout, together with supplementary material in the appendix. The review grew out of lecture notes and studies undertaken while learning the subject as a graduate student. Its aim is to provide an accessible and coherent introduction to modern holography, bridging the conceptual foundations of the AdS/CFT correspondence with several of its most important contemporary developments and open questions.