The paper discusses the development and significance of quantum error correction, a critical component for the practical realization of quantum computers. Quantum computers are more susceptible to errors compared to classical computers due to their sensitivity to environmental interactions. The key challenge is to protect quantum information from these errors, which can accumulate over time and lead to significant decoherence. The author highlights the progress made in quantum error correction, including the discovery of quantum error-correcting codes and the development of fault-tolerant recovery procedures. These procedures ensure that errors can be detected and corrected without causing further damage to the quantum state. The paper also introduces the concept of an accuracy threshold, which is the maximum error rate that can be tolerated before the quantum computation fails. For a quantum computer with about 1 million qubits and an error rate of \(10^{-9}\) per gate, the accuracy threshold would enable it to perform complex computations reliably. The paper reviews the basic elements of fault-tolerant computation, including the laws that must be followed to ensure reliable error recovery, such as avoiding using the same qubit multiple times, copying errors rather than data, verifying the correctness of operations, and using the right code. It also provides an example of Steane's 7-qubit code, which can correct single errors and is used to demonstrate how quantum error correction works in practice. Finally, the paper discusses the concept of concatenated codes, which can further improve the accuracy threshold by dividing the computational task into smaller, more manageable blocks. This allows for more efficient error correction and enables the performance of arbitrarily long quantum computations with a negligible probability of error. The paper concludes by emphasizing the importance of these advancements in making quantum computing a viable and practical technology.The paper discusses the development and significance of quantum error correction, a critical component for the practical realization of quantum computers. Quantum computers are more susceptible to errors compared to classical computers due to their sensitivity to environmental interactions. The key challenge is to protect quantum information from these errors, which can accumulate over time and lead to significant decoherence. The author highlights the progress made in quantum error correction, including the discovery of quantum error-correcting codes and the development of fault-tolerant recovery procedures. These procedures ensure that errors can be detected and corrected without causing further damage to the quantum state. The paper also introduces the concept of an accuracy threshold, which is the maximum error rate that can be tolerated before the quantum computation fails. For a quantum computer with about 1 million qubits and an error rate of \(10^{-9}\) per gate, the accuracy threshold would enable it to perform complex computations reliably. The paper reviews the basic elements of fault-tolerant computation, including the laws that must be followed to ensure reliable error recovery, such as avoiding using the same qubit multiple times, copying errors rather than data, verifying the correctness of operations, and using the right code. It also provides an example of Steane's 7-qubit code, which can correct single errors and is used to demonstrate how quantum error correction works in practice. Finally, the paper discusses the concept of concatenated codes, which can further improve the accuracy threshold by dividing the computational task into smaller, more manageable blocks. This allows for more efficient error correction and enables the performance of arbitrarily long quantum computations with a negligible probability of error. The paper concludes by emphasizing the importance of these advancements in making quantum computing a viable and practical technology.