This text defines the path integral and illustrates its uses by example. Suitable for advanced undergraduates and graduate students, its sole prerequisite is a first course in quantum mechanics. The first part develops the techniques of path integration. Numerous considerations include vector potentials, functional derivatives and commutation relations, and perturbation theory and Feynman diagrams. The second section, dealing with applications, covers a host of situations, including those related to the WKB approximation and near caustics; scattering theory; relativistic propagators and black holes; instantons and metastability; and the phase space path integral. 1981 ed. Indexes. 26 figures.