This review discusses the quantum interface between light and atomic ensembles, focusing on various mechanisms for quantum state transfer, entanglement generation, and quantum memory. The field has evolved from early studies of cavity quantum electrodynamics (QED) to more recent approaches involving atomic ensembles, which offer a powerful alternative to cavity-enhanced interactions with single atoms. Key mechanisms include quantum nondemolition (QND) interactions, quantum measurement and feedback, Raman interactions, photon echo, and electromagnetically induced transparency (EIT). The paper provides a theoretical framework for these processes, describes experimental techniques and media used for quantum interfaces, and reviews key experiments on quantum memory for light, quantum entanglement between atomic ensembles and light, and quantum teleportation with atomic ensembles. The review discusses two important quantum interface routines: quantum state transfer from light to atoms (quantum memory for light) and generation of entanglement between light and atoms. These routines enable quantum entanglement between remote atomic ensembles, atomic teleportation, and entanglement swapping. The quantum interface can be implemented either via direct interaction or through teleportation-like procedures involving entanglement generation, Bell measurement on light, and quantum feedback onto atoms. The paper also discusses the two main types of quantum measurements important for the interface: homodyne detection and photon counting. Homodyne detection provides continuous variable outcomes, while photon counting yields discrete variable results. The review concludes with an outlook on the future of atomic ensembles as an enabling technology in quantum information processing. The paper includes a detailed theoretical background, covering the description of light and atoms, the interaction of light with model atoms, and the theory including spontaneous emission. It also discusses the reduction of three-dimensional Hamiltonians to one dimension and the equations of motion for the beam splitter, parametric gain, and Faraday interactions. The review highlights the importance of the coupling constant κ in characterizing the strength of the interaction and discusses the role of spontaneous emission in the overall theory.This review discusses the quantum interface between light and atomic ensembles, focusing on various mechanisms for quantum state transfer, entanglement generation, and quantum memory. The field has evolved from early studies of cavity quantum electrodynamics (QED) to more recent approaches involving atomic ensembles, which offer a powerful alternative to cavity-enhanced interactions with single atoms. Key mechanisms include quantum nondemolition (QND) interactions, quantum measurement and feedback, Raman interactions, photon echo, and electromagnetically induced transparency (EIT). The paper provides a theoretical framework for these processes, describes experimental techniques and media used for quantum interfaces, and reviews key experiments on quantum memory for light, quantum entanglement between atomic ensembles and light, and quantum teleportation with atomic ensembles. The review discusses two important quantum interface routines: quantum state transfer from light to atoms (quantum memory for light) and generation of entanglement between light and atoms. These routines enable quantum entanglement between remote atomic ensembles, atomic teleportation, and entanglement swapping. The quantum interface can be implemented either via direct interaction or through teleportation-like procedures involving entanglement generation, Bell measurement on light, and quantum feedback onto atoms. The paper also discusses the two main types of quantum measurements important for the interface: homodyne detection and photon counting. Homodyne detection provides continuous variable outcomes, while photon counting yields discrete variable results. The review concludes with an outlook on the future of atomic ensembles as an enabling technology in quantum information processing. The paper includes a detailed theoretical background, covering the description of light and atoms, the interaction of light with model atoms, and the theory including spontaneous emission. It also discusses the reduction of three-dimensional Hamiltonians to one dimension and the equations of motion for the beam splitter, parametric gain, and Faraday interactions. The review highlights the importance of the coupling constant κ in characterizing the strength of the interaction and discusses the role of spontaneous emission in the overall theory.