  We review selected results for Higgs boson production at Linear Colliders in
the framework of the general Two-Higgs-Doublet Model (2HDM). We concentrate on
the analysis of i) the pairwise production of neutral Higgs bosons (hA,HA); and
ii) the neutral Higgs boson-strahlung modes (hZ, HZ). We identify sizable
production rates, in the range of 10-100 fb for center-of-mass energies of 0.5
TeV, alongside with large quantum effects (up to 50 %), which we can
fundamentally track down to the enhancement power of the triple-Higgs
self-interactions. This constitutes a telltale signature of the 2HDM, with no
counterpart in e.g. the Minimal Supersymmetric Standard Model (MSSM). We
compare these results with several complementary double and triple Higgs-boson
production mechanisms at order O(\alpha^3_{ew})-O(\alpha^4_{ew} and spotlight a
characteristic phenomenological profile which could eventually be highly
distinctive of a non-supersymmetric two-Higgs-doublet structure.
