This book is an introduction to holographic interferometry - a field of holography having a great number of important and practically useful ap­ pl ications. It is intended for special ists working in the field of optics and holography, and also for students of the relevant specialities. At present, a gr eater and greater number of mechanica 1 engi neers, tur­ bine designers, testers of diverse equipment, biologists, crystallographers, and so on have to do with holographic interferometry. To allow these spe­ cialists, who are comparatively far from optics, to master the subject too, the main content of the book is preceded by an introductory chapter treating the fundamental concepts of the interference of light, optical interferometry, holography and holographic interferometry. The following chapters deal with the fundamentals of the theory of ho­ lographic interferometry and of experimental equipment. The authors have set themselves the task of sharing their more than ten year of experience of work in the field of holographic interferometry with their readers. In this connection, the questions which they dealt with directly are con­ sidered in somewhat greater detail, as a rule, than those with which they have become acquainted only from publications on the subject. A sufficiently detailed (although far from complete) bibliography gives any interested reader an opportunity to improve his knowledge of this field.