  This article is the author's PhD thesis. After a review of string vacua
obtained through compactification (with and wothout fluxes), it presents and
describes various aspects of the Landscape of string vacua. At first it gives
an introduction and an overview of the statistical study of the set of four
dimensional string vacua, giving the detailed study of one corner of this set
(G2-holonomy compactifications of M-theory). Then it presents the ten
dimensional approach to string vacua, concentrating on the ten dimensional
description of the Type IIA flux vacua. Finally it gives two examples of models
having some interesting and characteristic phenomenological features, and that
belong to two different corners of the Landscape: warped compactifications of
Type IIB String Theory and M-theory compactifications on G2-holonomy manifolds.
