Herein, fiber hosts and rare earth gain ions commonly used in 3-μm fiber lasers are introduced, and the working principle of 3-μm rare earth ion-doped fiber lasers is briefly analyzed. Further, research progress on various 3-μm rare earth ion-doped fiber lasers is reviewed, revealing that mode-locked mid-infrared fiber lasers, miniaturized mid-infrared all-fiber lasers, and mid-infrared fiber lasers with long wavelengths of 3-4 μm are currently hot research topics. With the rapid development of 3-μm mid-infrared fiber lasers in recent years, 3-μm fiber lasers with a compact structure and excellent performance are emerging, which will greatly promote their commercialization and practical application in addition to fulfilling the requirements of different fields.