  These lectures provide an introduction to perturbative string theory and its
construction on spaces with background Ramond flux. Traditional covariant
quantization of the string and its connection with vertex operators and
conformal invariance of the worldsheet theory are reviewed. A supersymmetric
covariant quantization of the superstring in six and ten spacetime dimensions
is discussed. Correlation functions are computed with these variables.
Applications to strings in anti-de Sitter backgrounds with Ramond flux are
analyzed. Based on lectures presented at the Theoretical Advanced Study
Institute TASI 2001, June 3-29, 2001.
