We review the performances of few-mode in-line fiber amplifiers for mode division multiplexed transmission systems. We have experimentally demonstrated that differential modal gain (DMG) of <2 dB can be achieved amongst the guided modes using ring shaped erbium doping profile. The amplifier provides >20 dB small signal gain for all the guided modes with a gain flatness of ≤4.0 dB over the full C-band. Numerical modelling suggests that the DMG can be reduced to <1 dB by adopting complex doping profiles with the complexity rises as the number of guided modes increases. We have also reported the experimental demonstration of a few mode amplifier at the emerging telecommunication window of 2 μm supporting 3 spatial modes.