This three-volume ground-breaking and comprehensive bibliography of Irish texts and manuscripts is the first study of its kind to describe the entire historical and literary output of Irish writers, at home and abroad, throughout the middle ages (4th to 17th centuries). It surveys writers in Latin and the vernaculars, ranging through biblica, liturgica, computistica, hagiographica and grammatica, as well as all the genres of Irish and the other vernacular writings of Ireland. The focus is on both individual manuscripts and textual transmission. In the case of manuscripts it succinctly lists all the salient information (origin, provenance and date, foliation, pagination and dimensions), accompanied by a detailed chronologically arranged bibliography for every codex. For individual texts it lists the manuscripts in which they occur, or, when relevant, where such a list can be found, together with a comprehensive bibliography of relevant publications. For both manucripts and texts, there are running cross-references to the standard works of reference. The Index Manuscriptorum is the most comprehensive of its type ever provided for this subject. Moreover, the chapters on manuscripts and texts written in Irish provide the first full treatment of several areas, including annals, genealogies, vernacular law, early poetry, bardic poetry and metrics.