Optical fibers designed to support multiple transverse modes offer opportunities to study wave propagation in a setting that is intermediate between single-mode fiber and free-space propagation. To date, virtually all mode-locked lasers are based on resonators that support a single transverse spatial mode. Recently, the first reports of locking of multiple transverse and longitudinal modes of a fiber laser have been reported [1]. The variety of lasing states, and the potential for complete 3-dimensional control of a lasing field provide new research opportunities. The peak power of spatiotemporally-mode-locked lasers scales faster than the core area, which should lead to unprecedented performance from fiber lasers. The basic concepts of spatiotemporal mode-locking will be explained, and opportunities for future work will be outlined.