  The element Vub of the CKM mixing matrix is the smallest of the quark
couplings and is crucial in understanding CP violation in the B system. In this
review, we discuss the present status of the determination of its magnitude,
which involves a significant effort both experimentally and theoretically.
Decisive progress has been achieved in recent years, thanks in part to the
large data sets that have become available at the B factories. Based on these
data we propose an average |Vub| value of (3.67 \pm 0.47)x10^{-3}, which has an
uncertainty of 13%. With the experimental and theoretical progress expected in
the next few years a determination to an accuracy of 10%, or better, seems
feasible.
