The article by V. Vedral explores the role of relative entropy in quantum information theory, emphasizing its importance in understanding the limits of quantum information processing and communication. The review begins with an introduction to quantum mechanics and information theory, highlighting their interconnectedness and the unique insights they offer into the nature of information and computation. The concept of distinguishability, which underpins both fields, is discussed, and the relative entropy is introduced as a key measure of distinguishability. The author then delves into the properties of relative entropy, proving that it does not increase over time, which has significant implications for the evolution of quantum states. This principle is used to derive optimal bounds on the speed-up that quantum computers can achieve compared to classical computers. The review also covers various applications of relative entropy, including quantum communication, quantum computation, and quantum measurement. Key topics include Holevo's bound, Schumacher's compression, dense coding, and the thermodynamics of information erasure. The article further discusses the quantification of entanglement, teleportation, and the measures of entanglement derived from relative entropy. The role of measurement in quantum mechanics and its connection to thermodynamics and information theory is also explored. The review concludes with a discussion on the ultimate limits of computation, such as the Bekenstein bound, and the implications of quantum information theory for understanding the fundamental properties and limitations of nature.The article by V. Vedral explores the role of relative entropy in quantum information theory, emphasizing its importance in understanding the limits of quantum information processing and communication. The review begins with an introduction to quantum mechanics and information theory, highlighting their interconnectedness and the unique insights they offer into the nature of information and computation. The concept of distinguishability, which underpins both fields, is discussed, and the relative entropy is introduced as a key measure of distinguishability. The author then delves into the properties of relative entropy, proving that it does not increase over time, which has significant implications for the evolution of quantum states. This principle is used to derive optimal bounds on the speed-up that quantum computers can achieve compared to classical computers. The review also covers various applications of relative entropy, including quantum communication, quantum computation, and quantum measurement. Key topics include Holevo's bound, Schumacher's compression, dense coding, and the thermodynamics of information erasure. The article further discusses the quantification of entanglement, teleportation, and the measures of entanglement derived from relative entropy. The role of measurement in quantum mechanics and its connection to thermodynamics and information theory is also explored. The review concludes with a discussion on the ultimate limits of computation, such as the Bekenstein bound, and the implications of quantum information theory for understanding the fundamental properties and limitations of nature.