Quantum information is a rapidly emerging field aiming at combining two of the greatest advances in science and technology of the twentieth century, that is, quantum mechanics and information science. To reliably generate, store, process, and transmit quantum information, diverse systems have been studied. % ranging from natural system, e.g., photons, atoms, and spins, to %artificial systems, e.g., superconducting and nanomechanical structures. While for specific tasks some of these systems better suited than others, no single system can answer all envisioned demands. Erbium doped crystal has optical transition at 1.5 $\mu$m and possess long optical and spin coherence times, and are thus among the best candidates in building several essential blocks for quantum information applications. In this paper, the applications of erbium doped crystals in quantum memories, quantum transducers, quantum sources, and quantum manipulations based erbium-erbium interactions are summarized. Lastly, outlooks for near term prospects of the mentioned topics are given.