Our main result is a proof of the Florent Hivert conjecture [F. Hivert, Local action of the symmetric group and generalizations of quasi-symmetric functions, in preparation] that the algebras of r-Quasi-Symmetric polynomials in x 1 , x 2 , . . . , x n are free modules over the ring of Symmetric polynomials. The proof rests on a theorem that reduces a wide variety of freeness results to the establishment of a single dimension bound. We are thus able to derive the Etingof-Ginzburg [P. Etingof, V. Ginzburg, On m-quasi-invariants of a Coxeter group, Mosc. Math. J. 2 (2002) 555-566] Theorem on m-Quasi-Invariants and our r-QuasiSymmetric result as special cases of a single general principle. Another byproduct of the present treatment is a remarkably simple new proof of the freeness theorem for 1-Quasi-Symmetric polynomials given in [A.M. Garsia, N. Wallach, Qsym over Sym is free, J.We begin by fixing notation and recall some basic facts. We will throughout set X n = {x 1 , x 2 , . . . , x n } and denote by F[X n ] the algebra of polynomials in x 1 , x 2 , . . . , x n with coefficients in a field F of characteristic zero. If V is a graded vector space we denote by H m (V) the subspace of homogeneous elements of degree m in V. We then have the direct sum decomposition