During the last two decades more and more universities offer courses on modern structural reliability theory. A course on structural reliability theory is now a natural part of the curri­ culum for mechanical and structural engineering students. As a result of this, a number of textbooks have been published in this decade. In PlOst of these books it is shown how the reliability of single structural members can be evaluated in a rational way. The methods used are usually so-called level 2 methods, i. e. methods involving certain approximate iter­ ative calculations to obtain an approximate value of the probability of failure of the structural members. In these methods the joint probability distribution of relevant variables (re­ sistance variables, loads, etc. ) is simplified and the failure criteria are idealized in such a way that the reliability calculations can be performed without an unreasonable amount of work. In spite of the approximations and idealizations made it is believed that a rational treatment of uncertainties in structural engineering can be obtained by level 2 methods. Usually, in­ sufficient data are at hand to make a more advanced estimate of the reliability of a structural member. It has been recognized for many years that a fully satisfactory estimate of the reliability of a structure must be based on a systems approach. In some situations it is sufficient to estimate the reliability of the individual structural members of a structural system.