  We introduce a method for the study of CP-violating asymmetries in tagged
states of neutral $B$ mesons with arbitrary coherence properties. A set of
time-dependent measurements is identified which completely specifies the
density matrix of the initial state in a two-component space with basis vectors
$B^0$ and $\overline B^0$, and permits a determination of phases in the
Cabibbo-Kobayashi-Maskawa matrix. For a given tagging configuration, the
measurement of decays both to flavor eigenstates and to CP eigenstates provides
the necessary information.
