- The historiography of history writing in Ireland
- The history of the Irish Franciscan collection of manuscripts and rare books
- The intellectual history of medieval and early modern Ireland: creating a lexicon
- The impact of the mendicant orders on vernacular literature in late medieval Ireland
- The establishment of metropolitan episcopal sees in 12th-century Ireland: a comparative approach
- Kingship in late prehistoric and early medieval Ireland in a world context
- The landscape of kingship in early medieval Ireland
- Death and burial in early Ireland: a multi-disciplinary humanities and scientific model
Books edited & co-edited:
2011 The landscape of kingship and cult: text and archaeology (Four Courts Press, Dublin). Edited with Dr Roseanne Schot & Conor Newman, NUIG.
2009 The Irish Franciscans 1534-1990 (Four Courts Press, Dublin). Edited with Dr John McCafferty, UCD & Rev Dr Joseph MacMahon OFM.
2007 The Four Masters and their world (Wordwell Books, Dublin). Edited with Dr Bernadette Cunningham, Royal Irish Academy.
2005 The kingship and landscape of Tara (Discovery Programme/Four Courts Press, Dublin).
Chapters in books and collected essays:
2009 Ireland, c. 900-c.1000. In P. Stafford (ed.), A companion to the early Middle Ages: Britain and Ireland, c. 500–1100, 269-85. (Blackwell Publishers, Oxford).
2008 The Claidh Dubh: a study in the function and reuse of a prehistoric linear earthwork. In M. Doody (ed.), The Ballyhoura Hills project, 571-88. (Discovery Programme/Wordwell Books, Dublin).
2007 Perceptions of kingship in early medieval Irish vernacular literature. In L. Doran & J. Lyttleton (eds), Lordship in medieval Ireland. Image and reality, 21-46. (Four Courts Press, Dublin).
2004 Medieval sub-kingdoms of Brega: the kingships of Calatruim, Déssi Breg, Mugdornae Breg and Uí Maic Uais Breg. In A. Mac Shamhráin (ed.), The Island of St Patrick. Church and ruling dynasties in Fingal and Meath, 400-1148, 38-51. (Four Courts Press, Dublin).
2003 (with R. Ó Floinn) Ireland: culture and society. In S.H. Rigby (ed.), A companion to Britain in the later Middle Ages, 558–95. (Oxford).
2011 The friars and the vernacular in the Irish tradition. Irish Historical Studies 147 (2011), 357-75.
2006 In retrospect: introduction to George Petrie’s ‘On the History and Antiquities of Tara Hill’. Proceedings of the Royal Irish Academy 106, 409–16.
2003 Tales of Connacht: Cath Airtig, Táin Bó Flidhais, Cath Leitreach Ruibhe, and Cath Cumair. Cambrian Medieval Celtic Studies 45, 21–45.
2001 Review article: medieval Irish history at the end of the twentieth century: unfinished work. Irish Historical Studies 32, 260–71.
1999 Columban churches in Brega and Leinster: relations with the Anglo-Normans. Journal of the Royal Society of Antiquaries of Ireland 129, 5–18.
1996 Temoria: caput Scottorum? Ériu 47, 67–88.
1994 Killeshin: an Irish monastery surveyed. Cambridge (Cambrian) Medieval Celtic Studies 27, 33–47.
2011-12 ‘An image of Ireland and the world’: a quantification of contents and feasibility study of the medieval and early modern archive and library of the Irish Franciscan archive (Funded by the Andrew W. Mellon Foundation, New York)
2011-13 Monastic Ireland: a portal into the monastic foundations of Ireland, 1100-1500 AD (Funded by the Department of Arts, Heritage and the Gaeltacht, Dublin; Fáilte Ireland; University College Dublin)
2008 – Mapping Death, 1st to 8th centuries: boundaries, territories and people in Ireland/ Converting the Isles, 400-800 www.mappingdeathdb.ie (Funded by the Heritage Council INSTAR Programme, University College Dublin, Leverhulme Trust (with the University of Cambridge)