  We study the general properties of the freezeout of a thermal relic. We give
analytic estimates of the relic abundance for an arbitrary freezeout process,
showing when instantaneous freezeout is appropriate and how it can be corrected
when freezeout is slow. This is used to generalize the relationship between the
dark mater mass and coupling that matches the observed abundance. The result
encompasses well-studied particular examples, such as WIMPs, SIMPs,
coannihilation, coscattering, inverse decays, and forbidden channels, and
generalizes beyond them. In turn, this gives an approximate perturbative
unitarity bound on the dark matter mass for an arbitrary thermal freezeout
process. We show that going beyond the maximal masses allowed for freezeout via
dark matter self-annihilations (WIMP-like, $m_{\rm DM}\gg\mathcal{O}(100~\rm
TeV)$) predicts that there are nearly degenerate states with the dark matter
and that the dark matter is generically metastable. We show how freezeout of a
thermal relic may allow for dark matter masses up to the Planck scale.
