There are two types of cover which may typically be found on a book, primary and secondary. The primary cover is the material that constitutes the immediate covering of the completed binding, but not including additional, secondary, covers such as chemises or decorated paper over a plain primary cover. For inboard bindings, the primary covering material is used to cover the boards and spine, either completely, as in full bindings, or partially, as in half and quarter bindings. In all case bindings, and bindings with external sewing supports and longstitch bindings, the case itself may also be the covering material, and thus serve a dual function as both primary covering (which therefore may be given a secondary, decorated cover) and structural component. A secondary cover can be added in addition to a primary cover (but cannot be a secondary cover unless there is a primary cover already in place), either as protection or further embellishment of the book. In the latter case they are often made from decorated materials (most often textile or paper), but purely protective secondary covers can be made made from plain materials such as tanned or alum-tawed skins or paper, or recycled paper or parchment. They may be contemporary with and part of a complete binding, or may have been added afterwards (sometimes many years afterwards) to suit the taste and needs of a later owner. Many bindings with primary covers in parchment also have a lining of white paper under the parchment, intended both to brighten the parchment and make it opaque and also to soften the parchment with the moisture from the adhesive used to stick together so that it could be moulded around the book. Such linings on Dutch laced-case bindings with boards were adhered to the fleshside of the parchment before the book was covered, and could not be described as primary covers, but linings on Dutch inboard bindings of the seventeenth and eighteenth centuries were usually adhered to the book before the parchment was adhered around it. Such lining could therefore be thought of as primary covers, but their intended use as a lining and the fact that they would never have been left as covers in themselves means that they should always be thought of as a lining of the primary cover and not as an actual primary cover. Some bindings with embroidered covers may have similar linings.
et bokbind kan ha to typer overtrekk, det primære overtrekket befinner seg nærmest bokblokken, mens det sekundære er trukket utenpå det primære