The mid-infrared fiber lasers in the 2–3.5 μm spectral regions have been extensively applied in many application fields, such as biomedicine, telecommunications, military and nonlinear optics. With the improvements of the fiber components, the pumping regimes and other related technologies, the mid-infrared fiber lasers have made significant progress over the past decades and gradually become comparable with or supersede the traditional lasers in terms of certain lasing performance. In this review, from the beginning with the overview of fiber materials for the mid-infrared regions, we briefly summarize and review the latest research progress of mid-infrared continuous-wave (CW) and short pulse fiber lasers, including Tm³⁺-, Ho³⁺-doped, Tm³⁺-Ho³⁺ co-doped silicate fiber lasers for the 2 μm region and Er³⁺-, Ho³⁺-doped, Ho³⁺-Pr³⁺ co-doped ZBLAN fiber lasers for the 2.8–3.5 μm region. The advances of saturable absorbers applied in the mid-infrared pulse fiber lasers are also explored. Finally, the future prospects and challenges concerning the further development of mid-infrared fiber lasers are discussed and highlighted.