https://brill.com/view/title/34638

In this book Elizabeth Walgenbach argues that outlawry in medieval Iceland was a punishment shaped by the conventions of excommunication as it developed in the medieval Church. Excommunication and outlawry resemble one another, often closely, in a range of Icelandic texts, including lawcodes and narrative sources such as the contemporary sagas. This is not a chance resemblance but a by-product of the way the law was formed and written. Canon law helped to shape the outlines of secular justice.
The book is organized into chapters on excommunication, outlawry, outlawry as secular excommunication, and two case studies—one focused on the conflicts surrounding Bishop Guðmundr Arason and another focused on the outlaw Aron Hjǫrleifsson.