Design for Mechanical Fatigue deals with the complex process of failure of metals when subjected to variable repetitive loading over large numbers of operating cycles. Failure under these conditions can occur at loading levels significantly below the static strength capability of the material and can be catastrophic. The progression of a fatigue failure is a complex series of additive events. The information presented in this monograph is representative of the models and their application that are generally accepted as providing a reasonable estimate of predicting fatigue behavior. Chapter 1 includes testing for fatigue "strength", how life cycles are dependent on loading, modeling this relationship and consideration of physical factors that reduce ideal fatigue "strength" test results Chapter 2 deals with fatigue failure prediction under repetitive one-dimensional variable normal stress or shear stress states. This covers how these repetitive loadings are classified, establishing a failure theory based on the load classification, material properties, physical observations and conservative limitations. Chapter 3 deals with how the one-dimensional stress models are extended to cover simultaneous multiple stress loadings. A six-step process is presented that makes use of principal and Von Misses stresses together with the one dimensional failure theory. Chapter 4 considers estimating partial fatigue damage and damage accumulation when loading is changed during life cycle operation. The Palmgren-Miner Summation Theory and the Mason Modification of this approach is presented to illustrate how this issue can be addressed and how the results vary. Numerical solutions to example problems are included in each chapter. Approximately one third of the monograph's content consists of graphical and mathematical presentations to help explain and provide for a more complete understanding of the subject content.