Manuscripts and Archives are grouped together into Collections based on who created them, not their topic. For example, even though Special Collections might have five photograph albums of historic Newark Delaware pictures, we would not put them all together into a collection called "Newark Delaware Photographs." Instead, we would make one collection per creator. Archivists call this organizational principle provenance.
Each Collection is kept in its original order whenever possible. For example, when Special Collections gets the literary papers of an author, we do not rearrange them. We keep them in the same order that the creator had them in, because the arrangement itself might reveal valuable information about how the author worked. Archivists call this organizational principle original order.
When original order doesn't make sense, a Collection is sorted into types of material. For example, if Special Collections got the personal papers of an author and they weren't in any particular order to begin with, we would put together the correspondence, drafts, photographs, etc. into groupings called "Series." The items within these Series might be further sorted into alphabetical and/or chronological order.
Example of a typical arrangement:
Manuscript and archival collections are usually described in Finding Aids.
Finding Aid - 1. A tool that facilitates discovery of information within a collection of records. – 2. A description of records that gives the repository physical and intellectual control over the materials and that assists users to gain access to and understand the materials. (Online Glossary of Archival Terms, Society of American Archivists)
A finding aid describes where an archival collection came from, gives a synopsis of the creator's history, and provides an inventory of the collection. This is an example of the "Collection Contents" section of a Finding Aid:
Video courtesy of San Diego State University Library Infodome.