The gauge/gravity correspondence is a powerful tool to study non-perturbative physics of gauge theories in diverse dimensions. The holographic description of fundamental matter with a small number of flavours, Nf << Nc, is given by Nf probe D-branes in the appropriate gravitational background. I will discuss some general properties of the meson spectrum and thermal phase transitions in these theories. The talk is based on hep-th/0605046 and hep-th/0605017.