This dissertation provides critical editions of two medieval Irish aideda (‘death-tales’): Aided Ailella ⁊ Chonaill Chernaig (‘The Death-Tale of Ailill and Conall Cernach’) and Aided Cheit maic Mágach (‘The Death-Tale of Cet mac Mágach’). The editions are accompanied by translations, textual notes and linguistic analyses, followed by discussions of the textual traditions of both tales and literary commentary. The thesis consists of two parts. Part I, entitled Texts & Traditions, introduces the manuscripts in which the tales are contained: both tales are preserved in Edinburgh, National Library of Scotland, Adv. MS 72.1.40, while another copy of Aided Ailella ⁊ Chonaill Chernaig is found in Dublin, Trinity College Dublin, MS 1319. Following Thomas Owen Clancy, it is argued that the former manuscript is of particular interest, since the gathering in which the two tales are found consists of a collection of seven Ulster Cycle aideda. These constitute an independent thematic unit that should be read as an anthology of aideda. An examination of the evidence for the compilation and transmission of the group is provided, tracing the existence of the collection back to the twelfth or possibly tenth century. This is followed by a thematic analysis of the aideda anthology, arguing that the group of aideda constitutes a narrative cycle based on its generic unity. Following on from this discussion of manuscript context, linguistic analyses of both tales are presented, each followed by the edited text and translation. Any textual ambiguities, problematic forms or interpretational issues are discussed in the textual notes. The second part of the dissertation, which is entitled Context & Commentary, is split into two sections. The first section examines how the two extant aideda relate to references to the deaths of Ailill mac Máta, Conall Cernach and Cet mac Mágach in other sources, shedding light on the traditions that surround the deaths of these literary characters. It is demonstrated that the narrative tradition of the death of Conall is depicted relatively uniformly across all sources, and shows a particular connection to East Bréifne. References to the deaths of Cet and Bélchú reveal that the traditions of their deaths may have undergone changes, pertaining specifically to the setting of the narrative and the character of Bélchú, who may once had a different role. The second section presents an analysis of the literary themes and motifs that appear in both tales, focussing in particular on interpreting the narratives as part of the aideda anthology in the Edinburgh manuscript. It is argued that the placement of Aided Chonchobair within the aideda anthology impacts upon the interpretation of the group, and that the tales should be read as anti-heroic tales. The tales depict Irish heroic society as one of dysfunction and self-destruction, caused by the tragic breakdown of the relationships upon which this society was founded. The literary commentary examines how these traditional relationships in Aided Ailella ⁊ Chonaill Chernaig and Aided Cheit maic Mágach are subverted, leading to social chaos and disorder.