  The short range parts of the strong and weak hyperon-nucleon interactions are
studied with quark substructure of the baryons taken into account. A summary of
the quark cluster model calculations of the baryon-baryon interactions is
presented. It is pointed out that the spin-flavor symmetry structure determines
the qualitative behaviors of the short-range YN interactions. We also show that
the spin-orbit YN forces give characteristic behaviors, which are distinct from
the meson exchange forces. Weak decays of $\Lambda$ in hypernuclei are
described by the direct quark mechanism. We find that the neutron induced
nonmesonic decay is enhanced due to the direct quark transition. Importance of
the $\Delta I=3/2$ decay amplitudes is emphasized both for the nonmesonic weak
decays and the $\pi^+$ emission in the $\Lambda$ decay.
