This article reviews the progress in quantum information based on continuous quantum variables, with a focus on quantum optical implementations using the quadrature amplitudes of the electromagnetic field. The authors highlight the advantages of continuous variables, such as high efficiency and unconditionalness in generating and manipulating quantum states, particularly in the context of quantum communication protocols. They discuss the theoretical foundations of continuous variables, including quadratures, phase-space representations, Gaussian states, and linear and nonlinear optics. The article also explores various quantum information protocols, such as quantum teleportation, dense coding, quantum error correction, and quantum cryptography, emphasizing the role of continuous variables in these protocols. Additionally, it covers quantum cloning, quantum computation, and experimental demonstrations of quantum states and effects, such as quantum teleportation, entanglement swapping, and quantum memory. The review concludes with a discussion of the strengths and limitations of continuous-variable approaches in quantum information processing.This article reviews the progress in quantum information based on continuous quantum variables, with a focus on quantum optical implementations using the quadrature amplitudes of the electromagnetic field. The authors highlight the advantages of continuous variables, such as high efficiency and unconditionalness in generating and manipulating quantum states, particularly in the context of quantum communication protocols. They discuss the theoretical foundations of continuous variables, including quadratures, phase-space representations, Gaussian states, and linear and nonlinear optics. The article also explores various quantum information protocols, such as quantum teleportation, dense coding, quantum error correction, and quantum cryptography, emphasizing the role of continuous variables in these protocols. Additionally, it covers quantum cloning, quantum computation, and experimental demonstrations of quantum states and effects, such as quantum teleportation, entanglement swapping, and quantum memory. The review concludes with a discussion of the strengths and limitations of continuous-variable approaches in quantum information processing.