This paper will describe one instance of the system of Theme in Japanese as it is realised in a set of selected written texts. The unit over which Theme/Rheme is mapped is the Theme unit which is defined grammatically as a co-referential unit in which the referent is the first constituent (Thomson, 2005:162), and semantically as one phase of continuous thematic progression (Thomson, 2005:165). The realisation of Theme is the constituent in first position of the Theme unit. The following description includes a treatment of single Themes, multiple Themes, implicit Themes and marked Themes.