It is well known that the second stage of factoring methods that exploit smoothness of group orders can be implemented efficiently using the fast Fourier transform (FFT). For Pollard's p−1 method [17] this originated with the Mont-gomery and Silverman paper [16], and for the elliptic curve factoring method [12] it was the subject of Peter Montgomery's PhD dissertation [14]. Along with Peter's most recent work on this subject [15], these developments are presented in this chapter.