EISPACK is a collection of Fortran 66 subroutines for computing eigenvalues and eigenvectors of matrices. It contains 58 subroutines and 13 drivers. The subroutines are the basic building blocks for eigensystem computations; they perform such tasks as reduction to Hessenberg matrices (used for computing eigenvalues), computation of some or all of the eigenvalues/vectors, and back transformations, for various types of matrices.