This work is an English translation of the original Japanese, first published in 1993, but with extra chapters on fatigue failure of steels and the effect of surface roughness on fatigue strength. The first part of this book includes a concise explanation of metal fatigue. The methodology employed is based on important and reliable experimental results and may be usefully applied to other fatigue problems not directly treated in the book. The second half mainly addresses problems related to the influence of nonmetallic inclusions. This includes the introduction of an inclusion rating method based on the statistics of extremes, which will be useful not only for fatigue strength evaluation but also for making improvements in steel processing and material quality control. Engineers and researchers involved in the study of metal fatigue should find this work useful for solving practical problems in industry and developing new laboratory research.