  The reaction $ e^+e^- \to W^+W^-$ produces a $W$-boson pair with a
non-trivial spin correlation at threshold. This correlation leads to a
characteristic angular correlation between the leptons produced in $W^{\pm} \to
\ell ^{\pm} \nu$ (angles relative to the $e^-$ beam direction): $d \sigma /d
\cos \theta_+ d \cos \theta_- \sim (1-\cos \theta_+) (1+ \cos \theta_-) (1+\cos
\theta_- \cos \theta_+) $ . If only the $\ell^-$ is observed, its angular
distribution is $d \sigma / d \cos \theta_- \sim (1+\cos \theta_-)(3-\cos
\theta_-) $, implying a forward-backward asymmetry of 3/8. An analytic result
is also given for the azimuthal correlation. These results are reproduced by a
Monte Carlo program, that also enables us to study the effects of the $W$ decay
width. The threshold behaviour, which stems from the dominance of
$\nu$-exchange, is contrasted with that due to $\gamma$- and $Z$-exchange,
which is relevant for annihilation in the helicity state $e^-_Re^+_L$.
