This invaluable volume comprises the lecture notes of the 2001 School of the Theoretical Advanced Study Institute (TASI 2001). Intended mostly for advanced graduate students in theoretical physics, it presents a rare blend of formal and phenomenological topics, ranging from a thorough exposition of the minimal supersymmetric standard model to an exploration of modern topics in string field theory. Particular attention is given to the physics of extra dimensions, including possible experimental signatures, and to supersymmetric gauge theories and their relation to string theory in negatively curved backgrounds. The topics are rounded out by lectures on cosmology and on QCD at high density. The lecturers are exceptional leaders in their fields.