The argument made in this essay is that it is necessary to theorize a form of assessment--the academic viva in higher education. It is threatened with extinction because of its high cost compared with written exams, multiple choice and other forms of assessment. However, little empirical research, both in Norway and internationally, has been undertaken to reveal what is actually going on in the viva. This has partly been because it has been difficult to gain access to systematically observe the viva examination as it takes place. In the qualitative research presented by the author, on the higher education viva in Norway, permission was obtained to film a number of master's in education vivas where candidates defended 50,000-word dissertations. Three research questions were asked: how was the viva talked into being, what kinds of judgements were made by examiners, and, lastly, what would a validity argument look like for the viva? Answering these research questions moves some way to proposing a theory of the viva and hence providing a foundation for determining whether its continued existence is legitimate, at least from a theoretical and qualitatively researched point of view. (Contains 1 figure and 7 notes.)