  The Belle II experiment is a substantial upgrade of the Belle detector and
will operate at the SuperKEKB energy-asymmetric $e^+e^-$ collider. The design
luminosity of the machine is 8$\times10^{35}$ cm$^{-2}$s$^{-1}$ and the Belle
II experiment aims to record 50 ab$^{-1}$ of data, a factor of 50 more than its
predecessor. From February to July 2018, the machine has completed a
commissioning run and main operation of SuperKEKB has started in March 2019.
Belle II has a broad $\tau$ physics program, in particular in searches for
lepton flavor and lepton number violations (LFV and LNV), benefiting from the
large cross section of the pairwise $\tau$ lepton production in $e^+e^-$
collisions. We expect that after 5 years of data taking, Belle II will be able
to reduce the upper limits on LFV and LNV $\tau$ decays by an order of
magnitude. Any experimental observation of LFV or LNV in $\tau$ decays
constitutes an unambiguous sign of physics beyond the Standard Model, offering
the opportunity to probe the underlying New Physics. In this talk we will
review the $\tau$ lepton physics program of Belle II.
