  In this Thesis, we focus on the study of the low energy approximation to
non-critical string theories. We present an exhaustive study of their
solutions, which are divided in three cases: vacuum, NSNS charged, and RR
charged solutions. In the first case, we find all possible solutions, including
the previously known ones, which are special cases of ours. In the second case,
we present the fundamental non-critical string, doubly localized in Minkowski
\times the cigar vacuum. There are only a few known solutions doubly localized.
Also, we completely solve the problem of finding NSNS solutions that fill all
the Minkowski space. In the third case, we present new parametric families that
contain some of the previously known solutions at particular values of the
parameters. For the latter families, we have obtained the gauge duals in the
context of the gauge/gravity duality, and we show that, in a particular region
of the parameter space, these theories can confine. Finally, we study the
obtained YM in D=3 and YM in D=4 theories, and we show the corresponding
glueball spectra, that are in very good agreement with those predicted by
lattice QCD.
