Linear optical quantum computing uses single photons, linear optical elements, and projective measurements to achieve scalable quantum computing. The Knill-Laflamme-Milburn (KLM) protocol demonstrates that efficient quantum computing is possible with these components. Subsequent improvements have bridged the gap between theory and practice. This review discusses the original theory, improvements, and experimental implementations of optical quantum computing. It covers the use of realistic components, error correction, and the challenges of implementing scalable quantum circuits. The review also explores the use of projective measurements to induce nonlinearity, which is essential for creating entangled states. The paper discusses various protocols, including the KLM protocol, cluster state quantum computing, and error correction techniques. It highlights the importance of photon detection, photon sources, and quantum memories in practical implementations. The review concludes with an outlook on future developments in optical quantum computing, including photonic band-gap structures and hybrid matter-photon systems. The paper emphasizes the role of linear optics in quantum computing and the challenges of achieving deterministic quantum gates. It also discusses the use of nonlinearities, such as cross-Kerr effects, to enable quantum computing with photons. The review provides a comprehensive overview of the current state of linear optical quantum computing and its potential for future advancements.Linear optical quantum computing uses single photons, linear optical elements, and projective measurements to achieve scalable quantum computing. The Knill-Laflamme-Milburn (KLM) protocol demonstrates that efficient quantum computing is possible with these components. Subsequent improvements have bridged the gap between theory and practice. This review discusses the original theory, improvements, and experimental implementations of optical quantum computing. It covers the use of realistic components, error correction, and the challenges of implementing scalable quantum circuits. The review also explores the use of projective measurements to induce nonlinearity, which is essential for creating entangled states. The paper discusses various protocols, including the KLM protocol, cluster state quantum computing, and error correction techniques. It highlights the importance of photon detection, photon sources, and quantum memories in practical implementations. The review concludes with an outlook on future developments in optical quantum computing, including photonic band-gap structures and hybrid matter-photon systems. The paper emphasizes the role of linear optics in quantum computing and the challenges of achieving deterministic quantum gates. It also discusses the use of nonlinearities, such as cross-Kerr effects, to enable quantum computing with photons. The review provides a comprehensive overview of the current state of linear optical quantum computing and its potential for future advancements.