  The $\Lambda$-$\Lambda$ effective interaction, in the channel $L=S=0$, in the
nuclear medium is fitted to the available binding energies,
$B_{\Lambda\Lambda}$, of double $\Lambda$ hypernuclei:
$^{6}_{\Lambda\Lambda}$He, $^{10}_{\Lambda\Lambda}$Be and
$^{13}_{\Lambda\Lambda}$B. The mesonic decay of these hypernuclei is also
investigated. Finally, this effective interaction is used to predict the
binding energies and mesonic decays widths of heavier double $\Lambda$
hypernuclei.
