  We overview recent advances in the research on spatiotemporal beam shaping in
nonlinear multimode optical fibers. An intense light beam coupled to a graded
index (GRIN) highly multimode fiber undergoes a series of complex nonlinear
processes when its power grows larger. Among them, the lowest threshold effect
is the Kerr-induced beam self-cleaning, that redistributes most of the beam
energy into a robust bell-shaped beam close to the fundamental mode. At higher
powers a series of spectral sidebands is generated, thanks to the phase
matching induced by the long period grating due to the periodic self-imaging of
the beam and the Kerr effect. Subsequently a broadband and spectrally flat
supercontinuum is generated, extending from the visible to the mid-infrared.
