  The paper is concerned with the problem of determining a complete set of
invariants for output feedback. Using tools from geometric invariant theory it
is shown that there exists a quasi-projective variety whose points parameterize
the output feedback orbits in a unique way. If the McMillan degree $n\geq mp$,
the product of number of inputs and number of outputs, then it is shown that in
the closure of every feedback orbit there is exactly one nondegenerate system.
