  We extend the resummation of dimensionally-regulated amplitudes to
next-to-next-to-leading poles. This requires the calculation of two-loop
anomalous dimension matrices for color mixing through soft gluon exchange.
Remarkably, we find that they are proportional to the corresponding one-loop
matrices. Using the color generator notation, we reproduce the two-loop
single-pole quantities H^(2) introduced by Catani for quark and gluon elastic
scattering. Our results also make possible threshold and a variety of other
resummations at next-to-next-to leading logarithm. All of these considerations
apply to 2 to n processes with massless external lines.
