Starting with version 1.2, and up through version 1.15, Macaulay2 incorporated pari, a free library for fast computations in number theory, available at http://pari.math.u-bordeaux.fr/, originally developed by Henri Cohen and his co-workers at Université Bordeaux I, France. In the stated versions, it is used by factor(ZZ), factor(QQ), isPseudoprime, and isPrime(ZZ).