String theory is one of the most exciting and challenging areas of modern theoretical physics. This book guides the reader from the basics of string theory to recent developments. It covers many topics including world-sheet supersymmetry, space-time supersymmetry, conformal field theory, the heterotic string, string geometry and flux compactifications, and Matrix theory. This book is ideal for graduate students and researchers in modern string theory, and will make an excellent textbook. It contains exercises with solutions, and homework problems with solutions available to lecturers at www. cambridge. org