This thesis focuses on the development, from pre-Edo to modern times, of Japan's two main traditions of calligraphy- namely wayo (Japanese style) and karayo (Chinese style). Emphasis has been placed on the Edo period, in which both the wayo and karayo traditions were practised by large numbers of calligraphers, but discussions of the calligraphy practised in pre-Edo times, and in the Meiji and Modern periods, have also been included so as to provide appropriate context. In each period examined, reasons behind the development of wayo and karayo calligraphy have been considered. This is carried out in two ways: firstly, through a general investigation of the calligraphy practised in Japan during each period, and secondly, through the translation and analysis of a number of excerpts from treatises on calligraphy written by Japanese calligraphers. Finally, in the conclusion, reasons for and influencing factors behind the popularity of both wayo and karayo calligraphy in the periods examined are discussed.