We present a general description of electron spin polarization observed for interacting radical pairs. Unlike previous treatments, both chemically induced dynamic electron polarization and correlated radical pair polarization are included for ST0 mixing. A key feature of this model is that the members of the pair can remain interacting throughout the time sequence of electron spin polarization. Explanations of the time-dependent evolution of the electron spin polarization are presented using the density matrix and its associated vector diagram. A new vector method is formulated for calculating and visualizing chemically induced electron spin polarization. The approach is based on the vector, Δρ(t) which represents the displacement of the density vector ρ(t) from its direction at the time of its ‘‘birth.’’ In addition, these electron spin polarization phenomena are described in spectroscopic terms as well as in the usual mathematical manner.