  I first introduce the importance of measuring V_ub precisely. Then, from a
theoretician's point of view, I review (a) past history, (b) present trials,
and (c) possible future alternatives on measuring |V_ub| and/or |V_ub/V_cb|. As
of my main topic, I introduce a model-independent method, which predicts
\Gamma(B -> X_u l \nu) / \Gamma(B -> X_c l \nu) \equiv (\gamma_u / \gamma_c)
\times | V_{ub} / V_{cb}|^2 \simeq (1.83 \pm 0.28) \times |V_ub / V_cb|^2 and
|V_ub/V_cb| \equiv (\gamma_c / \gamma_u)^{1/2} \times [{\cal{B}}(B -> X_u l
\nu)/{\cal{B}}(B -> X_c l \nu)]^{1/2} \simeq (0.74 \pm 0.06) \times
[{\cal{B}}(B -> X_u l \nu)/ {\cal{B}}(B -> X_c l \nu)]^{1/2}, based on the
heavy quark effective theory. I also explore the possible experimental options
to separate B -> X_u l \nu from the dominant B -> X_c l \nu: the measurement of
inclusive hadronic invariant mass distributions, and the `D - \pi' (and `K -
\pi') separation conditions. I also clarify the relevant experimental
backgrounds.
