  Here we review a universal model for chirally induced spin-selectivity (CISS)
as a standalone effect occurring in chiral molecules. We tie together the
results of forward scattering in the gas phase to the results for
photoelectrons in chiral self-assembled monolayers and the more contemporary
results in two terminal transport setups. We discuss the ingredients that are
necessarily present in all experiments to date, which we identify as: i)
chirality, be it point, helical or configurational, ii) the spin-orbit coupling
as the spin active coupling of atomic origin, iii) decoherence as a
time-reversal symmetry breaking mechanism that avoids reciprocity relations in
the linear regime and finally iv) tunneling that accounts for the magnitude of
the spin polarization effect. This proposal does not discard other mechanisms
that can yield comparable spin effects related to interactions of the molecule
to contacts or substrates that have been proposed but that are less universal
or apply to particular situations. Finally, we discuss recent results
suggesting CISS as a molecular phenomenon in the real of enantiomer
selectivity, coherent electron transfer, and spin effects in chiroptical
activity.
