In a long-haul and high-speed wavelength division multiplexing transmission system, fiber Raman amplifier distributing the gain within transmission fiber can ideally offer a better noise performance than an erbium doped fiber amplifier (EDFA), and the former allows for a much broader amplification bandwidth. The development of suitable high-power pump LDs sparked renewed interest. Researchers were quick to demonstrate some of the advantages that fiber Raman amplifier has over EDFA, particularly when the transmission fiber itself is turned into a Raman amplifier. This paper starts with the fundamental properties of stimulated Raman scattering. Then, the structure of Raman amplifier and the merits of distributing Raman gain along a transmission fiber are discussed. Finally, novel Raman pumping schemes that have recently been developed are introduced.