This presentation has two parts. The first half discusses the major factorization algorithms when ECM was discovered in 1985, stressing the similarities between ECM and P +- 1. The second half describes the recent discoveries of six large Mersenne factors using ECM on a network of PlayStations.

This is joint work with Joppe W. Bos, Thorsten Kleinjung, and Arjen K. Lenstra from EPFL.