Palaeography is the study of old (palaeo) writing (graphy). It is a core skill for those who work on written documents of all kinds. In addition to enabling us to read texts, the study of writing can be used to provide insights into the processes used to create a wide range of books and documents, the circumstances in which writing was produced, and the people responsible.
Palaeographers often collaborate with experts in other facets of manuscript (from manu by hand and scriptus written) production such as codicology or art history. Codicology is the study of books (codices) as physical objects, encompassing the materials from which they were made, how parts were compiled, and who was involved in those processes. Some manuscripts and documents contain decoration added by a trained artist and this has been of interest to art historians.
A fuller explanation by Prof. Teresa Webber is available here.