The studies on the phenomena of fatigue in metals, and especially on the formation and growth rate of cracks have been conducted in 1972-1974 with continued intensity. Their results contribute to expanding our knowledge and give us a new insight into the sphere of metal fatigue which is a highly interdiscipline field. This makes the continuous amending and modifying of books on metal fatigue a necessity, unfortunately often related with the not easy task of changing one's opinions and critical analysis of established earlier notions. These aims were my chief concern when preparing the present edition of my book in which I made use of carefully selected new information from 1972-1973 and partly 1974 reports. This new matter has been included in many instances just to signal new facts or findings, since the limited space did not allow me to give them the amount of consideration they deserve. The book has been further supplemented with the results of micrographic studies conducted in co-operation with J. Kozubowski for which lowe him special thanks. I am also indebted to Mr. H. Mughrabi from Stuttgart for allowing me to publish in this book his very interesting micrographs of dislocation structures. Finally I should like to express my sincere thanks to Mr. E. Lepa for his concern in producing a good English translation of my book.