This document contains a more detailed description of the ENZdiffraction theory and clarifies the special features and potential applications of the theory. The contents of this document are the following:  A short description of the basic diffraction integral  Zernike representation of pupil functions  The propagation from the pupil to the focal region  Solving the aberration retrieval problem using the ENZapproach  Advanced ENZtheory  A survey of the literature on the subject  Current research and future extensions of the ENZapproach  Application of the ENZapproach to acoustical diffraction problems (ANZ)  A listing of the ENZpublications For the details of the application of the theory like the numerical implementation, convergence issues, highnumerical aperture complications, vector diffraction theory etc., the reader can consult bibliographic references that are introduced in this text and in the bibliography section of this webpage.
