  Light transport in a highly multimode fiber exhibits complex behavior in
space, time, frequency and polarization, especially in the presence of mode
coupling. The newly developed techniques of spatial wavefront shaping turn out
to be highly suitable to harness such enormous complexity: a spatial light
modulator enables precise characterization of field propagation through a
multimode fiber, and by adjusting the incident wavefront it can accurately
tailor the transmitted spatial pattern, temporal profile and polarization
state. This unprecedented control leads to multimode fiber applications in
imaging, endoscopy, optical trapping and microfabrication. Furthermore, the
output speckle pattern from a multimode fiber encodes spatial, temporal,
spectral and polarization properties of the input light, allowing such
information to be retrieved from spatial measurements only. This article
provides an overview of recent advances and breakthroughs in controlling light
propagation in multimode fibers, and discusses newly emerging applications.
