This text, in a sense, continues the treatment of the earlier Volume 6 in the Springer Series on Wave Phenomena , titled Geometrical Optics of Inhomogenous Media , by analyzing caustics and their fields on the basis of modern catastrophe theory. This volume covers the key generalizations of geometrical optics related to caustic asymptotic expansions: The Lewis-Kravtsov method of standard functions; Maslov’s method of canoncial operators; Orlov’s method of interference integrals, as well as their modifications for penumbra, space-time, random and other types of caustics. All the methods are illustrated by worked problems concerning relevant wave-field applications.