The story of the discovery of quantisation and quanta begins with the numerous problems facing physicists at the end of the nineteenth century. A number of experimental results did not fit naturally into the scheme of classical physics. Among the most important of these was the spectrum of black-body radiation, which was being determined much more precisely experimentally in the last decade of the nineteenth century and which had to be explained theoretically. Important clues came from the pioneering studies of the origin of the Stefan-Boltzmann law and Wien's displacement law, the latter involving the clever use of dimensional methods.