Research in theoretical physics, to be carried out by one of the new Presidential Young Investigators for 1991, will deal with various topics in string theory. One of these topics is the problem of providing a full classical definition, and eventually a quantum-mechanical definition, of the theory. A second topic is the further development of matrix model ideas for string theory. String theory is a promising candidate for a theory of all the basic forces and all the elementary particles, so its further elucidation is quite important.
