No manual can provide the fatigue investigator with a complete step-by-step detailed procedure which is valid for the statistical planning of experiments whatever the situation. In fact, only certain very simple fatigue test programs fit precisely into the specific formats required for wellestablished planned experiments, such as the completely randomized design (CRD) and the randomized complete block (RCB) design, [1]. Generally these simple fatigue test programs pertain to either elementary comparative tests (for example, comparing the fatigue life of Material A versus Material B), or to quality assurance tests (namely, the generation of certain fatigue data under well-defined test conditions). On the other hand, most (exploratory) research programs involve one or more (sometimes subtle) constraints peculiar to the specific situation, that is, to the given material processing, specimen preparation, test machine, environment, or whatever. Such constraints often preclude elementary statistical analysis of the resulting data and may even present difficulties to a trained statistician, particularly if he is consulted only after the tests have been conducted. But whatever the nature and the complexity of the given fatigue test situation, there are certain design of experiments fundamentals which must appear in the planning and conduct of any competent experimental program. It is the objective of this chapter of the manual to state these fundamentals (presented in italics in the following paragraph) and to illustrate their application in a few example situations. For further specific references to the design of experiments, see Refs 2, 3, and 4.