  We report the results of a search for the neutrinoless double-$\beta$ decay
(0$\nu\beta\beta$) of $^{100}$Mo, using the NEMO-3 detector to reconstruct the
full topology of the final state events. With an exposure of 34.7 kg.y, no
evidence for the 0$\nu\beta\beta$ signal has been found, yielding a limit for
the light Majorana neutrino mass mechanism of $T_{1/2}(0\nu\beta\beta)>1.1
\times 10^{24}$ years (90% C.L.) once both statistical and systematic
uncertainties are taken into account. Depending on the Nuclear Matrix Elements
this corresponds to an upper limit on the Majorana effective neutrino mass of
$< m_{\nu} > < 0.3-0.9$ eV (90% C.L.). Constraints on other lepton number
violating mechanisms of 0$\nu\beta\beta$ decays are also given. Searching for
high-energy double electron events in all suitable sources of the detector, no
event in the energy region [3.2-10] MeV is observed for an exposure of 47 kg.y.
