  We investigate and elucidate the phase structure of QCD for general number of
flavors $N_F$ with Wilson quarks, varying $N_F$ from 2 up to 300. Based on
numerical results combined with the result of the perturbation theory we
propose the following picture: When $N_F \ge 17$, there is only a trivial fixed
point and therefore the theory in the continuum limit is trivial. On the other
hand, when $16 \ge N_F \ge 7$, there is a non-trivial fixed point and therefore
the theory is non-trivial with anomalous dimensions, however, without quark
confinement. Theories which satisfy both quark confinement and spontaneous
chiral symmetry breaking in the continuum limit exist only for $N_F \le 6$. We
also discuss the structure of the deconfining phase at finite temperatures for
the small number of flavors such as $N_F=2$ and 3, through a systematic study
of it for general number of flavors.
