Fawley, W.M. MOB01 FEL electron radiation undulator controls 2015 2015-12 Beginning with the classic 1981 work of Kroll-Morton-Rosenbluth (*), multiple generations of FEL scientists have studied and used experimentally undulator tapering to improve and optimize the radiation output of both amplifier and oscillator FELs. Tapering has undergone a renaissance of interest, in part to make possible TW instantaneous power levels from x-ray FELs. In this talk, I will give a highly personalized (and undoubtedly strongly biased) historical survey of tapering studies beginning with the ELF 35-GHz experiments at Livermore in the mid-1980's and continuing up to quite recent studies at the LCLS at both soft and hard x-ray wavelengths.