||These notes comprise an expanded version of the string theory lectures given by the author at the 31st British Universities Summer School on Theoretical Elementary Particle Physics (BUSSTEPP) which was held in Manchester, England in 2001. The school is attended mostly by Ph.D. students in theoretical high-energy physics who have just completed their first year of graduate studies at a British university. The lectures were thereby appropriately geared for this level. No prior knowledge of string theory was assumed, but a good background in quantum field theory, introductory level particle physics and group theory was. An acquaintance with the basic ideas of general relativity is helpful but not absolutely essential. Some familiarity with supersymmetry was also assumed because the supersymmetry lectures preceeded the string theory lectures at the school, although the full-blown machinery and techniques of supersymmetry were not exploited to any large extent.
The main references for string theory used during the course were the standard books on the subject [31, 47] and the more recent review article . The prerequisite super-symmetry lectures can be found in .* The lectures were delivered in the morning and exercises were assigned for the tutorial sessions which took place in the afternoons. These problems are also included in these notes. Many of them are intended to fill in the technical gaps which due to time constraints were not covered in the lectures. Others are intended to give the student a better grasp of some "stringy" topics. The present paper has expanded on many aspects of string theory that were addressed during the school, mainly to make the presentation clearer.