Towards a Complete Calculation of $γγ\to 4f$

We propose a general classification of all four fermion final states in $\gamma\gamma$ collisions at a future $e^+e^-$ Linear Collider and discuss the relation of ``signal'' and ``background'' contributions in vector boson production. We utilize the results in a critical examination of the Higgs signal in sub-threshold $W^+W^-$ pair production.