  In supersymmetric theories a field can develop a vacuum expectation value $M
\gg 10^3\,{\rm GeV}$, even though its mass $m$ is of order $10^2$ to
$10^3\,{\rm GeV}$. The finite temperature in the early Universe can hold such a
field at zero, corresponding to a false vacuum with energy density $ V_0 \sim
m^2 M^2 $. When the temperature falls below $V_0^{1/4}$, the thermal energy
density becomes negligible and an era of thermal inflation begins. It ends when
the field rolls away from zero at a temperature of order $m$, corresponding to
of order 10 $e$-folds of inflation which does not affect the density
perturbation generated during ordinary inflation. Thermal inflation can solve
the Polonyi/moduli problem if $M$ is within one or two orders of magnitude of
$10^{12}\,{\rm GeV}$.
