We review the possible role that multi-Higgs models may play in our
understanding of the dynamics of a heavy 4th sequential generation of fermions.
We describe the underlying ingredients of such models, focusing on two Higgs
doublets, and discuss how they may effectively accommodate the low energy
phenomenology of such new heavy fermionic degrees of freedom. We also discuss
the constraints on these models from precision electroweak data as well as from
flavor physics and the implications for collider searches of the Higgs
particles and of the 4th generation fermions, bearing in mind the recent
observation of a light Higgs with a mass of ~125 GeV.Comment: An invited review: to appear in a special issue of Advances in High
Energy Physics (AHEP) on Very Heavy Quarks at the LHC. Version 2: minor
change to title, reference list and last section updated. 32 pages, 24
figure
