We introduce the atomic-ensemble-based single-photon source. Thanks to the collective enhancement, It has the following advantages: it does not require strong coupling between light and matter, thanks to the collective enhancement; the generated narrow band single photons are storable, narrow-band, and highly controllable; and the single photons emitted from independent sources are pure and indistinguishable. In conjunction with a feedback circuit, the atomic-ensemble single-photon source can work in a deterministic way, where the production rate is significantly enhanced while low and good indistinguishability are preserved. The atomic-ensemble-based single-photon sources provide an essential tool for scalable quantum networks and linear-optical quantum computation.