Quantum entanglement is a fundamental property of quantum systems that allows for nonclassical correlations between subsystems. It was first recognized by Einstein, Podolsky, Rosen, and Schrödinger, and has since become a key resource in quantum information theory. This article reviews the basic aspects of entanglement, including its characterization, detection, distillation, and quantification. It discusses various manifestations of entanglement, such as Bell inequalities, entropic inequalities, entanglement witnesses, and quantum cryptography. The authors also emphasize the role of entanglement in quantum communication and highlight its unique properties, such as irreversibility and bound entanglement. Entanglement is a crucial resource for quantum technologies, enabling tasks such as quantum cryptography, teleportation, and dense coding. However, it is fragile and difficult to detect, requiring sophisticated tools and methods. The article explores the theoretical and experimental foundations of entanglement, including its connection to quantum mechanics, Bell's theorem, and the concept of separability. It also discusses the development of entanglement witnesses, which are essential for detecting entanglement in mixed states. The article covers various aspects of entanglement, including its role in quantum communication, the distinction between entangled and separable states, and the challenges of manipulating and measuring entanglement. It also addresses the concept of bound entanglement, which cannot be distilled into pure entangled states, and the importance of entanglement in quantum computing and information theory. The text highlights the significance of entanglement in quantum cryptography, where it enables secure communication protocols such as quantum key distribution. It also discusses the broader implications of entanglement in quantum mechanics, including its role in quantum computing, quantum teleportation, and the study of quantum phase transitions. The article provides a comprehensive overview of the current state of entanglement research, emphasizing its theoretical foundations, experimental verification, and practical applications. It underscores the importance of entanglement in advancing quantum technologies and highlights the ongoing challenges in understanding and utilizing this fundamental quantum resource.Quantum entanglement is a fundamental property of quantum systems that allows for nonclassical correlations between subsystems. It was first recognized by Einstein, Podolsky, Rosen, and Schrödinger, and has since become a key resource in quantum information theory. This article reviews the basic aspects of entanglement, including its characterization, detection, distillation, and quantification. It discusses various manifestations of entanglement, such as Bell inequalities, entropic inequalities, entanglement witnesses, and quantum cryptography. The authors also emphasize the role of entanglement in quantum communication and highlight its unique properties, such as irreversibility and bound entanglement. Entanglement is a crucial resource for quantum technologies, enabling tasks such as quantum cryptography, teleportation, and dense coding. However, it is fragile and difficult to detect, requiring sophisticated tools and methods. The article explores the theoretical and experimental foundations of entanglement, including its connection to quantum mechanics, Bell's theorem, and the concept of separability. It also discusses the development of entanglement witnesses, which are essential for detecting entanglement in mixed states. The article covers various aspects of entanglement, including its role in quantum communication, the distinction between entangled and separable states, and the challenges of manipulating and measuring entanglement. It also addresses the concept of bound entanglement, which cannot be distilled into pure entangled states, and the importance of entanglement in quantum computing and information theory. The text highlights the significance of entanglement in quantum cryptography, where it enables secure communication protocols such as quantum key distribution. It also discusses the broader implications of entanglement in quantum mechanics, including its role in quantum computing, quantum teleportation, and the study of quantum phase transitions. The article provides a comprehensive overview of the current state of entanglement research, emphasizing its theoretical foundations, experimental verification, and practical applications. It underscores the importance of entanglement in advancing quantum technologies and highlights the ongoing challenges in understanding and utilizing this fundamental quantum resource.