This review article, authored by Jian-Wei Pan, Zeng-Bing Chen, Chao-Yang Lu, Harald Weinfurter, Anton Zeilinger, and Marek Zukowski, provides a comprehensive overview of multi-photon interference and its applications in quantum mechanics and quantum information processing. The authors highlight the rapid advancements in both theoretical and experimental research, focusing on the creation of photonic entanglement, tests of quantum mechanics, quantum communication protocols, and quantum computation with linear optics. The article begins with an introduction to quantum optics, discussing the historical development of the field and the fundamental principles of quantum mechanics. It then delves into the differences between classical and quantum interference, emphasizing the rich and complex nature of quantum interference phenomena. The concept of entanglement is introduced, explaining its role in quantum mechanics and its implications for the EPR paradox and Bell's theorem. The review covers various sources of photonic entanglement, particularly spontaneous parametric down-conversion (SPDC), and the techniques used to create multi-photon entanglement, such as entanglement swapping. It also discusses the applications of multi-photon interference in quantum communication, including quantum key distribution, quantum teleportation, and quantum repeaters. Additionally, the article explores linear optical quantum computing, including the use of cluster states and one-way quantum computing. The authors conclude by discussing the future directions of research in multi-photon interferometry and quantum information processing, emphasizing the potential for further exciting developments in the field.This review article, authored by Jian-Wei Pan, Zeng-Bing Chen, Chao-Yang Lu, Harald Weinfurter, Anton Zeilinger, and Marek Zukowski, provides a comprehensive overview of multi-photon interference and its applications in quantum mechanics and quantum information processing. The authors highlight the rapid advancements in both theoretical and experimental research, focusing on the creation of photonic entanglement, tests of quantum mechanics, quantum communication protocols, and quantum computation with linear optics. The article begins with an introduction to quantum optics, discussing the historical development of the field and the fundamental principles of quantum mechanics. It then delves into the differences between classical and quantum interference, emphasizing the rich and complex nature of quantum interference phenomena. The concept of entanglement is introduced, explaining its role in quantum mechanics and its implications for the EPR paradox and Bell's theorem. The review covers various sources of photonic entanglement, particularly spontaneous parametric down-conversion (SPDC), and the techniques used to create multi-photon entanglement, such as entanglement swapping. It also discusses the applications of multi-photon interference in quantum communication, including quantum key distribution, quantum teleportation, and quantum repeaters. Additionally, the article explores linear optical quantum computing, including the use of cluster states and one-way quantum computing. The authors conclude by discussing the future directions of research in multi-photon interferometry and quantum information processing, emphasizing the potential for further exciting developments in the field.