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The non-perturbative dynamics of quantum field theories is studied usingtheoretical tools inspired by string formalism. Two main lines are developed:the analysis of stringy instantons in a class of four-dimensional N=2 gaugetheories and the holographic study of the minimal model for a strongly coupledunbalanced superconductor.  The field theory instanton calculus admits a natural and efficientdescription in terms of D-brane models. In addition, the string viewpointoffers the possibility of generalizing the ordinary instanton configurations.Even though such generalized, or stringy, instantons would be absent in apurely field-theoretical, low-energy treatment, we demonstrate that they doalter the IR effective description of the brane dynamics by introducingcontributions related to the string scale. In the first part of this thesis wecompute explicitly the stringy instanton corrections to the effectiveprepotential in a class of quiver gauge theories.  In the second part of the thesis, we present a detailed analysis of theminimal holographic setup yielding an effective description of a superconductorwith two Abelian currents. The model contains a scalar field whose condensationproduces a spontaneous symmetry breaking which describes the transition to asuperfluid phase. This system has important applications in both QCD andcondensed matter physics; moreover, it allows us to study mixed electric-spintransport properties (i.e. spintronics) at strong coupling.

D-branes and Non-Perturbative Quantum Field Theory: Stringy Instantons and Strongly Coupled Spintronics