The aim of the research group GAST is to contribute with original scientific work to the understanding of some of the key dynamical issues occurring in the field-theoretic and string-theoretic models of fundamental interactions. We address ourselves mainly to those areas of theoretical physics, whose importance grew considerably in the last few years, where gravity, string and gauge-field theories make contact, inspiring each other, providing exact solutions and giving important hints about their non-perturbative properties. Indeed, one of the most successful frameworks in this direction is the gauge-gravity correspondence that allows one to derive exact results in strongly interacting gauge theories by looking at string theories in the perturbative regime. On the other side, computations in gauge or in topological theories are instrumental in verifying conjectures about string dynamics and string dualities. The understanding of the non-perturbative dynamical properties is of course mandatory for realistic models as Quantum Chromodynamics, the theory of strong interactions, and for the composite models of "elementary particles". Moreover, the quantum description of black holes and the choice of the correct vacuum in string theories crucially need a non-perturbative analysis. There are common key ingredients, appearing in many different guises in the research projects covered by our group. These are the concept of solitons and their quantum behaviors, of instantons and moduli space; the topics of sigma models, topological field theories and matrix models; the chiral properties of supersymmetric gauge theories and conformal field theories; integrability as a bridge between weak and strong coupling behaviors of gauge theories. D-branes can also be considered as solitonic solutions of supergravity, the low energy limit of string theory, and the description of their dynamics and thermodynamics is of crucial importance for the application of string theory to real physical systems and, more generally, to gain understanding on the non-perturbative behavior of field theories.