This essay is intended to survey two broad issues which determine the use of textual data. The first is the underlying orientation towards the use of textual data and how this relates to critical evaluations of agency, authority and materiality. This essay surveys two broad orientations: (i) an essentially retrospective genetic orientation and, (ii) an orientation which focuses on the phenomenon of change. Both approaches are dependent on the ability to distinguish original readings from scribal readings, identify genetic relationships and account for acts of horizontal transmission. With this in mind, the second issue with which this essay is concerned is the importance of critical interpretation in the categorisation of textual data. This essay argues that textual criticism is a practical demonstration of the difficulties of interpretation and that no textual data ‘has any real evidential value until it has been interpreted’ (Patterson 90).