J. M. Sanz-Serna & M. P. Calvo, Numerical Hamiltonian Problems, Chapmand and Hall, London, 1994, ix+207 pp. This is a book Maripaz Calvo and I wrote in 1992-1993 to provide an easy account of the then emerging field of Geometric Integration. It was out of print for many years and a Dover edition has now appeared. At present it has more than 2000 citations in Google Scholar.