  X-ray observations of galaxies have grown from a curiosity into a
full-fledged field of astronomy. These observations provide unique information
on black holes, binary stars, and the hot phase of the ISM, which can be used
to constrain the chemical evolution of the Universe, and the joint evolution of
galaxies and massive black holes. These exciting results are due in large part
to the high-resolution capability of {\it Chandra}. To follow on {\it Chandra}
and push forward this science past the present capabilities, our community must
build a high-resolution (sub-arcsecond) large-area (several square meters)
X-ray telescope.
