Some Issues in Conformal Field Theory with Boundaries and Crosscaps

Abstract

This is a brief introduction to the subject of Conformal Field Theory on surfaces with boundaries and crosscaps, which describes the perturbative expansion of open string theory.

Invited talk given at the Conference `Conformal Field Theory and Integrable Systems', held by Landau Institute, Russia, September 15-21, 2002. Latex, 6 pages Some references added