Historical introduction and overview -- The classical closed bosonic string -- Free bosonic quantum field theory -- Covariant quantization -- Light-cone quantization -- Branes and quantization of open strings -- Open strings and gauge theory -- Supersymmetry in ten dimensions -- Construction of type IIA/B superstrings -- Branes in type II superstring theory -- Construction of heterotic superstrings -- Introduction to conformal field theory -- Modular invariants and orbifolds -- Closed strings on the 3-sphere -- Calabi-Yau spaces -- Calabi-Yau compactifications -- String dualities -- Gauge/string dualities -- AdS/CFT correspondence -- Epilogue: Strings and high energy scattering