  In this work, the moduli of D7-branes in type IIB orientifold
compactifications and their stabilization by fluxes is studied from the
perspective of F-theory. In F-theory, the moduli of the D7-branes and the
moduli of the orientifold are unified in the moduli space of an elliptic
Calabi-Yau manifold. This makes it possible to study the flux stabilization of
D7-branes in an elegant manner. To answer phenomenological questions, one has
to translate the deformations of the elliptic Calabi-Yau manifold of F-theory
back to the positions and the shape of the D7-branes. We address this problem
by constructing the homology cycles that are relevant for the deformations of
the elliptic Calabi-Yau manifold. We show the viability of our approach for the
case of elliptic two- and three-folds. Furthermore, we discuss consistency
conditions related to the intersections between D7-branes and orientifold
planes which are automatically fulfilled in F-theory. Finally, we use our
results to study the flux stabilization of D7-branes on the orientifold
$K3\times T^2/\Z_2$ using F-theory on $K3\times K3$. In this context, we derive
conditions on the fluxes to stabilize a given configuration of D7-branes. This
thesis furthermore contains an introduction to F-theory and a brief review of
some mathematical background.
