  When did the universe thermalize? In this talk I review the status of this
issue and its importance in establishing the expected properties of dark
matter, the growth of large-scale structure, and the viability of inflation
models when confronted with CMB observations. I also present a novel approach
to tackling the theoretical challenges surrounding inflationary (p)reheating,
which seeks to extend past work on the Effective Field Theory of Inflation to
the time of reheating.
