  In this paper a review of the LEP analyses on $B^0 - \bar{B}^0$ oscillations
and on the measurement of $|V_{ub}|/|V_{cb}|$ is presented . These measurements
are of fundamental importance in constraining the $\rho$ and $\eta$ parameters
of the CKM matrix. A review of the current status of the $V_{CKM}$ matrix
determination is also given.
