This text is aimed at practising engineers, particularly those within the areas of design, production and maintenance. It covers three crucial factors in the development and support of new or existing products; how reliable is the product; what are the costs of maintenance going to be; and what will the costs of supporting the product be once it is in the market place. The text uses simple mathematics that engineers should be able to use; probability. A software program, PROBCHAR, is packaged with the text, enhancing its appeal by allowing the engineer to use the book as a practical tool for the analysis of products through their life-cycle.