The first five years of operation of the two multi-purpose experiments ZEUS and H1 at the HERA electron--proton storage ring facility in Hamburg, Germany have opened a new era in the study of diffractive vector-meson production in high-energy photon--proton interactions. This book provides readers who have a general knowledge of the concepts and experimental techniques of elementary particle physics with the information necessary to assess the status of the new investigations prior to the end of 1996. The measurements are placed in the rich historical context of earlier studies of photo- and leptoproduction of vector mesons.