  We determine the Postnikov Tower and Postnikov Invariants of a Crossed
Complex in a purely algebraic way. Using the fact that Crossed Complexes are
homotopy types for filtered spaces, we use the above "algebraically defined"
Postnikov Tower and Postnikov Invariants to obtain from them those of filtered
spaces. We argue that a similar "purely algebraic" approach to Postnikov
Invariants may also be used in other categories of spaces.
