  We present an updated overview on the phenomenology of one-loop Higgs boson
production at Linear Colliders within the general Two-Higgs-Doublet Model
(2HDM). First we report on the Higgs boson pair production, and associated
Higgs-Z boson production, at O(alpha^3_{ew}) from e+e- collisions. These
channels furnish cross-sections in the range of 10-100 fb for Ecm=0.5 TeV and
exhibit potentially large radiative corrections (of order 50%), whose origin
can be traced back to the genuine enhancement capabilities of the triple Higgs
boson self-interactions. Next we consider the loop-induced production of a
single Higgs boson from direct gamma-gamma scattering. We single out sizable
departures from the corresponding rates in the Standard Model, which are again
correlated to trademark dynamical features of the 2HDM -- namely the balance of
the non-standard Higgs/gauge, Higgs/fermion and Higgs self-interactions leading
to sizable (destructive) interference effects. This pattern of quantum effects
is unmatched in the MSSM, and could hence provide distinctive footprints of
non-supersymmetric Higgs boson physics. Both calculations are revisited within
a common, brought-to-date framework and include, in particular, the most
stringent bounds from unitarity and flavor physics.
