  We consider the effects of fragmentation on the post-inflationary epoch of
reheating. In simple single field models of inflation, an inflaton condensate
undergoes an oscillatory phase once inflationary expansion ends. The equation
of state of the condensate depends on the shape of the scalar potential,
$V(\phi)$, about its minimum. Assuming $V(\phi) \sim \phi^k$, the equation of
state parameter is given by $w = P_\phi/\rho_\phi = (k-2)/(k+2)$. The evolution
of condensate and the reheating process depend on $k$. For $k \ge 4$, inflaton
self-interactions may lead to the fragmentation of the condensate and alter the
reheating process. Indeed, these self-interactions lead to the production of a
massless gas of inflaton particles as $w$ relaxes to 1/3. If reheating occurs
before fragmentation, the effects of fragmentation are harmless. We find,
however, that the effects of fragmentation depend sensitively to the specific
reheating process. Reheating through the decays to fermions is largely excluded
since perturbative couplings would imply that fragmentation occurs before
reheating and in fact could prevent reheating from completion. Reheating
through the decays to boson is relatively unaffected by fragmentation and
reheating through scatterings results in a lower reheating temperature.
