  Non-negligible dark energy density at high redshifts would indicate dark
energy physics distinct from a cosmological constant or ``reasonable''
canonical scalar fields. Such dark energy can be constrained tightly through
investigation of the growth of structure, with limits of \la2% of total energy
density at z\gg1 for many models. Intermediate dark energy can have effects
distinct from its energy density; the dark ages acceleration can be constrained
to last less than 5% of a Hubble e-fold time, exacerbating the coincidence
problem. Both the total linear growth, or equivalently \sigma_8, and the shape
and evolution of the nonlinear mass power spectrum for z<2 (using the
Linder-White nonlinear mapping prescription) provide important windows. Probes
of growth, such as weak gravitational lensing, can interact with supernovae and
CMB distance measurements to scan dark energy behavior over the entire range
z=0-1100.
