  Monopole dominance for the nonperturbative features in QCD is studied both in
the continuum and the lattice gauge theories. First, we study the dynamical
chiral-symmetry breaking (D$\chi $SB) in the dual Higgs theory using the
effective potential formalism. We find that the main driving force for D$\chi
$SB is brought from the confinement part in the nonperturbative gluon
propagator rather than the short-range part, which means monopole dominance for
D$\chi $SB. Second, the correlation between instantons and QCD-monopoles is
studied. In the Polyakov-like gauge, where $A_4(x)$ is diagonalized, the
QCD-monopole trajectory penetrates the center of each instanton, and becomes
complicated in the multi-instanton system. Finally, using the SU(2) lattice
gauge theory with $16^4$ and $16^3 \times 4$, the instanton number is measured
in the singular (monopole-dominating) and regular (photon-dominating) sectors,
respectively. Instantons and anti-instantons only exist in the monopole sector
both in the maximally abelian gauge and in the Polyakov gauge, which means
monopole dominance for the topological charge.
