Amazon.com description: Product Description: This session of the Les Houches Summer School was organized with two principal purposes. Firstly to introduce a common language and culture to a mixed audience, composed of field theorists, string theorists, condensed matter physicists and statistical mechanicians. Secondly, to expose young researchers to the recent advances in various areas of theoretical physics, where the concepts of extended objects, geometry and fluctuations are currently playing an important role. Courses included an introduction to the problem of random paths in disordered media; theoretical and numerical approaches to quantize geometries, from random paths to surfaces/strings to four-dimensional gravity; physics of amphiphilic membranes and the models of random surfaces used to describe them; defects in various physical systems; recent developments on the formulation of two dimensional gauge theories as string theories. Problems of condensed matter physics were surveyed and a seminar on the renormalization of interacting fermion models provided additional technical details. The course were followed by lectures covering conformal field theory and perturbative string theory and ended with the most pressing problems posed by our current lack of understanding of string theory.