In the last few years many important successes have been achieved in the understanding of string theory and its relation to large N gauge theories. The AdS-CFT proposal is the best understood example of such holographic dualities. Since its original propos al, many steps have been taken to extend this duality and build the string theory dual of (large N) QCD, but a satisfactory and complete model is still a long way to come. It is plausible that the dual of QCD involves a non-critical five-dimensional string theory. Compared to critical ten-dimensional theories, not much is known about non-critical strings, and only recently the extension of AdS-CFT to the non-critical case has been considered. The aim of the present project is to gain a deeper understanding in the duality between non-critical strings and four-dimensional gauge theories. Studying non-critical AdS-CFT will require understanding the way non-critical string theory behaves in the presence of background RR fluxes. This is an essential feature of al l dual string theories because D-branes (which sustain gauge and flavor degrees of freedom) are sources for RR-fields. Moreover, non-critical AdS-CFT will have to deal with stringy effects since the characteristic size of the backgrounds involved is of the same order as the string length. To this purpose, it will be very interesting to use the duality and known results on superconformal gauge theories to gain insights into string dynamics. We will also consider the breaking of the field theory conformal inv ariance: while at a first stage this symmetry proves to be very useful to constrain the dynamics of the system under consideration, QCD is not conformally invariant. In particular we will be interested in the effect on the string background, of D-branes ca rrying flavor degrees of freedom. We know that in general the presence of matter breaks conformal invariance of the gauge theory. This should be described by the back-reaction of flavor branes.