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Multimode fibers (MMFs) have attracted interest because of their larger mode area and additional spatial degrees of freedom compared with single-mode fibers. Recently, MMFs have been introduced into mode-locked lasers for new cavity structures with better laser performance. Among these lasers, there are two remarkable cases in which MMFs are the key components for mode-locking: One is using a short segment of the MMF as a saturable absorber (SA), which has the advantages of high damage threshold, wide operating bandwidth, and low cost. The other is the construction of multimode cavities with MMFs. Spatiotemporal mode-locking (STML), a general form of mode-locking, can be achieved in such cavities. Herein, we review these two types of mode-locked lasers with MMFs. The principles of MMF-based SA and STML are described based on the common theory of multimode nonlinear fiber optics …