  We study the polarization of the J/\psi meson of the B_c -> J/\psi mu nu
decay process, followed by J/\psi -> mu+ mu-, with the help of the heavy-quark
spin symmetry formalism (HQSS). We adapt the ISGW wave function. Due to the
clean signature of the decay mode, measurements of the polarization of the
J/\psi meson can play a special role in extracting |V_{cb}|, the quark
mixing-matrix element. We compare the results with the predictions of other
quark models.
