  We study the nature of the QCD vacuum at general number of flavors $N_F$ by
numerical simulations on the lattice. Combining the results with those of the
perturbation theory, we propose the following picture: 1) For $N_F \ge 17$,
there exists only one IR fixed point at vanishing gauge coupling, i.e., the
theory in the continuum limit is trivial. 2) For $16 \ge N_F \ge 7$, there is a
non-trivial fixed point. Therefore, the theory is non-trivial with anomalous
dimensions, however, without quark confinement. 3) For $N_F \le 6$, theories
satisfy both quark confinement and spontaneous chiral symmetry breaking in the
continuum limit.
