  A purely combinatorial construction of the quantum cohomology ring of the
flag manifold $G/B$ is presented. We show that the ring we construct is
commutative, associative and satisfies the usual grading condition. By using
results of two of our previous papers, we obtain a presentation of this ring in
terms of generators and relations, as well as formulas for quantum Giambelli
polynomials. We show that these polynomials satisfy a certain orthogonality
property, which - for G=SL_n(C) - was proved previously by Fomin, Gelfand and
Postnikov.
