9501018 Ooguri String theory is an attempt to move beyond the quantum mechanical description of elementary particles as point like particles to a formulation of them as excitations of a microscopic string-like object. These excitations would include not only quarks, gluons, leptons etc., but also the graviton, the quantum excitation of gravity so that one would have a truly unified theory. The ultimate aim of this research is a better and deeper understanding of space-time and a quantum theory of gravity. One approach has been to study string field theory, namely field theories of strings. ***