  A formalism is presented to evaluate the Sivers function in constituent quark
models. A non-relativistic reduction of the scheme is performed and applied to
the Isgur-Karl model. The results obtained are consistent with a sizable Sivers
effect and the signs for the u and d flavor contributions turn out to be
opposite. The Burkardt Sum Rule is fulfilled to a large extent. After the
estimate of the QCD evolution of the results from the momentum scale of the
model to the experimental one, a reasonable agreement with the available data
is obtained. A calculation of nuclear effects in the extraction of neutron
single spin asymmetries in semi-inclusive deep inelastic scattering off 3He is
also described. In the kinematics of forth-coming experiments at JLab, it is
found that the nuclear effects arising within an Impulse Approximation approach
are under control.
