  In models with a non-minimal Higgs sector, the lightest scalar state may be a
neutral CP-even Higgs boson, whose properties are nearly identical to those of
the minimal Higgs boson of the Standard Model. In such a scenario, the other
Higgs scalars are significantly heavier than $m_Z$; their effects rapidly
decouple from the low-energy theory. The decoupling limit of the most general
CP-conserving two-Higgs doublet model is formulated. Detection of evidence for
a non-minimal Higgs sector in the decoupling limit presents a formidable
challenge for Higgs searches at future colliders.
