  We investigate a method for determining the CP nature of a neutral Higgs
boson or spin-zero resonance at a future linear e+e- collider (ILC) in its tau
decay channel. Our procedure is applicable if the production vertex of the
Higgs boson can be measured. This will be the case, for example, for the
Higgs-strahlung process. We show that the method is feasible for both the
leptonic and the hadronic 1-prong tau decay modes.
