  We describe a simple and robust mechanism that stabilizes all Kahler moduli
in Type IIB orientifold compactifications. This is shown to be possible with
just one non-perturbative contribution to the superpotential coming from either
a D3-instanton or D7-branes wrapped on an ample divisor. This
moduli-stabilization mechanism is similar to and motivated by the one used in
the fluxless G_2 compactifications of M-theory. After explaining the general
idea, explicit examples of Calabi-Yau orientifolds with one and three Kahler
moduli are worked out. We find that the stabilized volumes of all two- and
four-cycles as well as the volume of the Calabi-Yau manifold are controlled by
a single parameter, namely, the volume of the ample divisor. This feature would
dramatically constrain any realistic models of particle physics embedded into
such compactifications. Broad consequences for phenomenology are discussed, in
particular the dynamical solution to the strong CP-problem within the
framework.
