A finding aid, in the context of archival science, is a document containing detailed information about a specific collection of records within an archive. They often consist of an inventory and description of the materials, their source, and their structure.  The finding aid for a collection is usually compiled by the collection's entity of origin, or by an archivist or librarian during archival processing, and serves the purpose of locating specific information within the collection.
As long as humans have stored documents, they have created tools to navigate their storage systems; ancient Sumerians created them to locate bureaucratic records.  In modern times, finding aids were paper documents such as lists or index cards; now they can be created in electronic formats like spreadsheets or databases. The standard machine-readable format for manuscript collection finding aids, widely used in the United States, Canada, the United Kingdom, France, Australia and elsewhere, is Encoded Archival Description. 
The content of a finding aid may differ depending on the type of material it is describing. Usually, a finding aid includes a description of the scope of the collection, biographical and historical information related to the collection, and restrictions on use of or access to the materials. Finding aids may be detailed inventories that list contents. They may also include subject headings drawn from LCSH, AAT, or other controlled vocabulary, and may cross-refer to related collections in other repositories. The data elements essential to finding aids are defined by the International Council on Archives in the General International Standard Archival Description (ISAD(G)). Various national implementations of ISAD(G) exist, such as Describing Archives: A Content Standard, used in the USA.
The process of creating a finding aid often begins with archival description. For example, Encoded Archival Description calls for a basic description of the collection, a list of controlled vocabulary terms, administrative information, biographical information, scope and content, arrangement, description of components, and other descriptive data.  In the absence of a universal standard for finding aids, these elements are often used as a basis.
The Basic Description, Collection Overview, or Summary Information is usually the first section of a finding aid, containing information about the collection's creator, the physical space the collection occupies in the archive, and the date range and an abstract of its documents. A Biographical/Historical Note describes a collection from the perspective of the time period it was created, providing background information on a person or organization. It can also describe the history of the collection. The Scope and Content note briefly explains the collection's provenance, its arrangement and date range, and in general what kind of materials it contains—letters, reports, photographs, audio/video, etc.
The Access and Use section that contains information about using the collection, such as terms of access and restrictions. Usage issues that may affect researchers. Usage issues that may affect researchers could include donor agreements restricting access, copyright information in the event the researcher wishes to publish items from the collection, the collection's history of ownership, any additional formats the collection may have, and if the collection is accepting additions. Additional Information contains details of related materials, language, citation instructions, any sponsors, and the date of processing. Search Terms are generally a list of subject headings, any personal, corporate, or family names, subject and geographical headings, and genre terms that relate to the contents of the collection. Arrangement is the manner in which the collection has been ordered.
The Content List is a list of the collection's materials down to the box and folder level. In a finding aid, the top level is the record group and within the record group are series descriptions containing the title, dates of coverage, and a brief description of the contents of each series. Series descriptions may also include the range of containers, a statement of the type of arrangement, and a note on any restrictions for each series.
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- Harmeyer, Neal. "Library Guides: Primary Sources in Archives & Special Collections: How to Read a Finding Aid". guides.lib.purdue.edu. Retrieved 2018-04-19.
- Harmeyer, Neal. "Library Guides: Primary Sources in Archives & Special Collections: How to Read a Finding Aid". guides.lib.purdue.edu. Retrieved 2018-04-05.
- Sections of a finding aid from Purdue University