  The Higgs trilinear coupling provides a unique opportunity to study the
structure of the Higgs sector and probe indirect signs of BSM Physics -- even
if new states are somehow hidden. In models with extended Higgs sectors, large
deviations in the Higgs trilinear coupling can appear at one loop because of
non-decoupling effects in the radiative corrections involving the additional
scalar states. It is then natural to ask how two-loop corrections modify this
result, and whether new large corrections can appear again. We present new
results on the dominant two-loop corrections to the Higgs trilinear coupling in
several models with extended scalar sectors. We illustrate the analytical
expressions with numerical examples and show that, while they remain smaller
than their one-loop counterparts and do not modify significantly the
non-decoupling effects observed at one loop, the two-loop corrections are not
entirely negligible -- a typical size being 10-20% of the one-loop corrections.
