Humfress has published widely on the history of late antiquity (c. 200–c. 600 AD) and is currently finishing a monograph, Multi-legalism in Late Antiquity, for Oxford University Press. She also has published on the history of empires, recently co-editing a volume on Law and Empire: Ideas, Practices, Actors. She also researches early Christian history and ecclesiastical law. Some of her recent research explores contemporary approaches to law and legal history within the disciplines of anthropology and sociology.
Her current international research projects include the European Commission-funded project, Power and Institutions in Medieval Islam and Christendom, and The Cambridge Comparative History of Ancient Law, the first project of its kind in the field of comparative ancient legal history, which involves working with an international team of scholars specializing in the fields of ancient Greek, Roman, Indo-European, Near-Eastern, and Chinese law.