  A lecture given at the International School Seminar on {\sl Hadrons and
Nuclei from QCD}, Tsuruga-Vladivostok-Sapporo, August-September, 1993.
  A realistic hyperon ($Y$)-nucleon ($N$) interaction based on the quark model
and the one-boson-exchange potential is constructed. The Nijmegen potential
model D with the SU(3) flavor symmetry is modified with a quark exchange
interaction at the short-distance, which replaces the short-range repulsive
core in the original model. The flavor-spin dependences of the short-range
repulsion are qualitatively different from the original hard-core potential. We
also study a two-body weak decay, $\Lambda N \to NN$, in the quark model. An
effective weak interaction, where one-loop QCD corrections are explicitly taken
into account, is employed. Differences from the conventional meson-exchange
processes are discussed.
