Quantum field theory and string theory are the tools of modern theoretical physics to investigate the most basic constituents and fundamental forces of Nature.

Field theory combines special relativity and quantum mechanics, and explains elementary particles as excitations of a field. At the same time it provides a universal language for describing extended physical systems, with dynamical objects in every point of space, and as a result it also finds applications to statistical and condensed matter physics.

String theory in addition combines general relativity, which describes the gravitational force, with quantum mechanics. Therefore it is also a promising theory as a candidate for a unified theory of all forces.

String theory and field theory are intimately linked to each other, and each of the two areas is useful for understanding aspects of the other.