Does a mystic, divine formula lie behind everything that is beautiful? For centuries the golden mean has been a subject of endless fascination. The ratio of the proportion can be seen in Nature; it runs through artistic design processes and it affects our perception of our surroundings. But how much of this apparent "world formula" is true, and how much of it is myth? The history of the golden mean begins with Euclid in the 3rd century BC. But it was only in the 19th century that it was raised to the universal constant of beauty. From this point onwards the "golden section" was described in flora and fauna; the famous Fibonacci number. It determines the growth of the pineapple; and Le Corbusier optimised architecture by means of the Modulor. But does this art-historical phenomenon really play a universal role in the organisation of our world? Authors from all fields analyse the Golden Mean with regard to function, demonstrability and relevance, also by means of current examples from art and design as well as in comparison with the DIN and the tatami measurement.