  We report current status of global analyses on nuclear parton distribution
functions (NPDFs). The optimum NPDFs are determined by analyzing high-energy
nuclear reaction data. Due to limited experimental measurements, antiquark
modifications have large uncertainties at x>0.2 and gluon modifications cannot
be determined. A nuclear modification difference between u and d quark
distributions could be an origin of the long-standing NuTeV sin^2 theta_w
anomaly. There is also an issue of nuclear modification differences between the
structure functions of charged-lepton and neutrino reactions. Next, nuclear
clustering effects are discussed in structure functions F_2^A as a possible
explanation for an anomalous result in the Be-9 nucleus at the Thomas Jefferson
National Accelerator Facility (JLab). Last, tensor-polarized quark and
antiquark distribution functions are extracted from HERMES data on the
polarized structure function b_1 of the deuteron, and they could be used for
testing theoretical models and for proposing future experiments, for example,
the one at JLab. Such measurements could open a new field of spin physics in
spin-one hadrons.
