ESDU 86013 discusses factors that affect the fatigue strength of a welded joint and, in particular, from fracture mechanics arguments, shows that the strength is independent of the strength properties of the parent material. Similar arguments show the likely effect of size is to reduce the fatigue strength over that found in smaller joints (such as laboratory specimens on which many of the fatigue data available depend). The influence of residual stresses, and in turn their effect on the way mean stress is experienced, is discussed, and the use of thermal stress relieving is considered. Various design options for joints are indicated, together with likely crack initiation sites in each case. A complete directory of some 30 possible types of welded joints for which fatigue data are included in other ESDU documents (ESDU 75016, ESDU 76007, ESDU 76032, ESDU 77011, ESDU 78016, ESDU 78023 and ESDU 81007) are listed together with their equivalent type and class of weld as defined in BS 5400.