This paper comprises the written version of the lectures on string theory delivered at the 31st British Universities Summer School on Theoretical Elementary Particle Physics which was held in Manchester, England, August 28 – September 12 2001.

The effective action for the local composite operator Φ2(x) in the scalar quantum field theory with λΦ4 interaction is obtained in the expansion in two-particle-point-irreducible (2PPI) diagrams up to fiveloops. The effective potential and 2-point Green’s functions for elementary and composite fields are derived. The ground state energy as well as oneand two-particle excitations are calculated ...

We give an elementary introduction to the theory of supermembranes. DEDICATED TO THE MEMORY OF ABDUS SALAM Based on lectures given at the T. A. S. I. Summer School, University of Colorado, Boulder, June 1996; the Topical Meeting, Imperial College, London, July 1996 and the 26th British Universities Summer School in Theoretical Elementary Particle Physics, University of Swansea, September 1996. ...

We give an elementary introduction to the theory of supermembranes. DEDICATED TO THE MEMORY OF ABDUS SALAM Based on lectures given at the T. A. S. I. Summer School, University of Colorado, Boulder, June 1996; the Topical Meeting, Imperial College, London, July 1996 and the 26th British Universities Summer School in Theoretical Elementary Particle Physics, University of Swansea, September 1996. ...