  In models with a non-minimal Higgs sector, a decoupling limit can be defined.
In this limit, the masses of all the physical Higgs states are large (compared
to the scale of electroweak symmetry breaking) except for one neutral CP-even
Higgs scalar, whose properties are indistinguishable from the Higgs boson of
the minimal Standard Model. The decoupling limit of the most general
CP-conserving two-Higgs doublet model is formulated. Detection of evidence for
a non-minimal Higgs sector at future colliders in the decoupling limit may
present a formidable challenge for future Higgs searches.
