  A consistent description of the radiative polarization for relativistic
electrons in intense laser fields is derived by generalizing the Sokolov-Ternov
effect in general field structure. The new form together with the
spin-dependent radiation-reaction force provides a complete set of dynamical
equations for electron momentum and spin in strong fields. When applied to
varying intense fields, e.g. the laser fields, the generalized Sokolov-Ternov
effect allows electrons to gain or lose polarization in any directions other
than along the magnetic field in the rest frame of the electron. The
generalized theory is applied to the collision process between initially
polarized/unpolarized high energy electrons with linearly polarized
ultra-intense laser pulse, showing results that eliminate the dependence on
specific choices of a quantization axis and spin initialization existing in
spin-projection models.
