  With the help of a simple variational procedure it is possible to convert the
partial sums of order $N$ of many divergent series expansions
$f(g)=\sum_{n=0}^\infty a_n g^n$ into partial sums $\sum_{n=0}^N b_n g^{-
\omega n}$, where $0<\omega<1$ is a parameter that parametrizes the approach to
the large-$g$ limit. The latter are partial sums of a strong-coupling expansion
of $f(g)$ which converge against $f(g)$ for $g$ {\em outside} a certain
divergence radius. The error decreases exponentially fast for large $N$, like
$e^{-{\rm const.}\times N^{1-\omega}}$. We present a review of the method and
various applications.
