The present study is the first large-scale investigation of the syntax of Old Japanese (mainly eighth-century Japanese). It gives a detailed account of complement clauses and related constructions in Old Japanese, based on an exhaustive investigation of the extant text corpus. The aim is twofold: first, to give a synchronic description of the types of complementation which are found in this period and of the system they are part of. Second, to address the diachronic issues of the origin of the Old Japanese complement system and more widely the pre-history of complementation in Japanese. Janick Wrona’s study will be of interest to historical linguists and Japanologists alike.