Generation and propagation of various soliton molecules (SMs) in fiber systems are reviewed. SMs can survive either in fibers or fiber lasers. A dispersion-managed (DM) fiber link is the only platform for SM demonstration, while various fiber lasers can support different SMs. The fundamental unit of SMs can be conventional solitons generated in an anomalous dispersion regime, stretched pulses in DM fiber lasers, parabolic pulses, or gain-guided solitons in a normal dispersion regime. SMs with typically close soliton separation are presented. In addition, we demonstrate a new kind of SM with nanosecond soliton separation. The narrow spectral filtering is required for the generation of SMs with such long-distance interaction.