Let M be a finitely generated module over a Noetherian ring R and N be a submodule. The index of reducibility ir M (N ) is the number of irreducible submodules that appear in an irredundant irreducible decomposition of N (this number is well defined by a classical result of Emmy Noether). Then the main results of this paper are:embedded component of N for all embedded associated prime ideals p i of N ; (3) For an ideal I of R there exists a polynomial Ir M,I (n) such that Ir M,I (n) = ir M (I n M ) for n 0. Moreover, bight M (I) − 1 ≤ deg(Ir M,I (n)) ≤ M (I) − 1; (4) If (R, m) is local, M is Cohen-Macaulay if and only if there exist an integer l and a parameter ideal q of M contained in m l such that ir M (qM ) = dim R/m Soc(H d m (M )), where d = dim M .