The first detailed studies of electronic components reliability were undertaken to improve the performance of communications and navigational systems used by the American army. The techniques then developed were subsequently refined and applied to equipment used for many other applications where high reliability was of paramount importance - for example in civil airline electronic systems. The evolution of good and reliable products is the responsibility of technical and professional persons, engineers and designers. These individuals cannot succeed unless they are given adequate opportunity to apply their arts and mysteries so as to bring the end-product to the necessary level of satisfaction. Few managements, however, are yet aware of the far greater potential value of the reliability of their products or services. Yet customer satisfaction depends, in most cases, far more on the reliability of performance than on quality in the industrial sense. There was a time when reliable design could be prescribed simply as "picking good parts and using them right". Nowadays the complexity of systems, particularly electronic systems, and the demand for ultrahigh reliability in many applications mean that sophisticated methods based on numerical analysis and probability techniques have been brought to bear - particularly in the early stages of design - on determining the feasibility of systems.