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Records Authority
Category: Archival Management

Accession Number

Also known as: AN, Catalogue Number, Accession Identifier
Simply put

An accession number is a unique identifier assigned to a group of materials when they are formally received into the care of an archive, library, museum, or similar repository. It works like a reference tag that lets the holding institution track and locate that set of materials. The exact form and rules for assigning these numbers vary by institution and by the type of collection involved.

Formal definition

In archival and collection management practice, an accession number is a unique identifier assigned to a body of materials at the point of accession, typically when those materials are transferred into the legal custody of a repository. For example, in the context of the U.S. National Archives it denotes the unique identifier assigned to a group of archival materials transferred into NARA's legal custody. The term is used more broadly across galleries, libraries, archives, and museums to identify accessioned objects or records, and analogous 'accession number' constructs appear in other domains such as bibliographic databases and biological sequence repositories, where they identify individual records rather than accessioned physical holdings. Practitioners should note that the accession number identifies the accessioned unit for control and tracking purposes and is distinct from later descriptive, classification, or arrangement identifiers; format conventions and assignment rules depend on the institution and its cataloguing scheme.

Why it matters

The accession number is a foundational control device: it establishes a fixed point of reference for a body of materials at the moment those materials enter a repository's care. Without a reliable identifier assigned at the point of accession, an institution cannot dependably track what it holds, demonstrate the chain of custody, or link physical or digital holdings back to the documentation created when they were received. In the context of archives such as the U.S. National Archives, the accession number identifies a group of materials transferred into the repository's legal custody, tying the holdings to the transfer event and the associated accountability that follows from taking custody.

The number matters most where evidential value and accountability are at stake. Because it is typically assigned at receipt and remains stable thereafter, the accession number supports tracking and location of materials independently of any later descriptive, classification, or arrangement work. This separation is significant: descriptive and cataloguing schemes may be revised, collections may be rearranged, and finding aids may change, but the accession number continues to identify the accessioned unit as it was received. Practitioners should be careful not to treat the accession number as though it were a descriptive or classification identifier, since conflating these functions can obscure the custodial record of what was actually received.

The term also travels across domains, which is a common source of confusion. Galleries, libraries, archives, and museums use accession or catalogue numbers to identify accessioned objects, while bibliographic databases and biological sequence repositories use 'accession number' constructs to identify individual records rather than accessioned physical holdings. Recognizing that these are analogous but distinct uses helps professionals avoid assuming that assignment rules, scope, or format from one context apply in another.

Who it's relevant to

Archivists and collection managers
For those responsible for receiving and controlling holdings, the accession number is a primary tool for tracking materials from the point of custody transfer onward. It supports location, control, and accountability, and should be maintained distinctly from later descriptive or arrangement identifiers so that the record of what was received remains stable.
Records managers overseeing transfers
Where records are transferred into the legal custody of an archive, the accession number links the transferred materials to the transfer event and to the receiving institution's custodial documentation. This is relevant when demonstrating chain of custody or coordinating disposition that involves transfer to a repository rather than destruction.
Librarians and museum registrars
Across galleries, libraries, archives, and museums, accession or catalogue numbers identify accessioned objects. Practitioners should be aware that assignment rules and formats vary by institution and by collection type, and that the number identifies the accessioned unit rather than serving as a descriptive record in itself.
Researchers and data professionals working across systems
Those who encounter 'accession number' in bibliographic databases or biological sequence repositories should note that in these contexts the number identifies an individual record within a system rather than an accessioned physical holding. Recognizing this distinction avoids misapplying conventions from one domain to another.

Inside AN

Unique identifier
A distinct code or number assigned to a body of records at the point of accession, used to differentiate it from all other accessions within the receiving repository.
Link to the accession record
The number typically serves as a key that connects the physical or digital materials to descriptive and administrative metadata held in an accession register or recordkeeping system.
Control and tracking function
The identifier supports intellectual and physical control by enabling the repository to locate, account for, and track the materials from the point of receipt through subsequent processing.
Association with a transfer or acquisition event
An accession number generally corresponds to a specific transfer, deposit, or acquisition event rather than to individual items, so a single number often covers a group of records received together.

Common questions

Answers to the questions practitioners most commonly ask about AN.

Is an accession number the same as a record's classification code or file reference?
No. An accession number typically identifies a specific transfer or acquisition of records into a repository's custody, whereas a classification code or file reference relates to how records are categorized by function, subject, or business activity. The two serve different purposes: one tracks the event and batch of intake, the other supports arrangement and retrieval. Depending on organizational policy, a set of records may carry both, and the accession number does not itself describe the content or context of the records in the way a classification scheme does.
Does assigning an accession number mean the records have been permanently preserved or archived?
Not necessarily. An accession number generally records that material has been taken into a repository's control at a point of transfer, but accession is a distinct step from appraisal, arrangement, description, and any decision about long-term preservation. Records may be accessioned and later subject to further disposition, which can include transfer elsewhere, permanent retention, or destruction under authorized schedules. The presence of an accession number should therefore not be read as confirmation of permanent archival status.
When should an accession number be assigned in the intake workflow?
In many repositories the accession number is assigned at the point records enter custody, so that the transfer is documented before further processing begins. Assigning it early can help establish an audit trail from the moment of receipt. Organizational policy and the practices of the relevant repository determine the exact timing, and workflows vary between institutions and jurisdictions.
What information is typically recorded alongside an accession number?
Practices vary, but an accession record often captures details such as the source or transferring body, the date of transfer, a description of the material received, its extent or quantity, and any conditions attached to the transfer. The specific fields depend on the repository's descriptive standards and organizational policy, and are intended to support later identification, control, and processing of the accessioned material.
How should accession numbers be structured to remain unique and stable?
Accession numbers are generally intended to be unique within a given repository and to remain stable once assigned, so that they can serve as persistent points of reference. Some organizations use sequential numbering, sometimes combined with a year or a repository identifier, but structures differ between institutions. The main considerations are avoiding duplication and not reusing numbers, so that the link between an identifier and a particular transfer is preserved.
How does an accession number relate to subsequent disposition actions?
An accession number can provide a reference point that ties a batch of records to later actions, so that decisions on retention, transfer, or destruction can be traced back to the original transfer. It does not by itself authorize or determine those actions, which typically depend on retention schedules, appraisal outcomes, and applicable requirements that vary by jurisdiction and sector. In practice the accession record often works alongside other control information to support accountable disposition.

Common misconceptions

An accession number is the same as a classification code or file reference.
An accession number identifies a body of records at the point of receipt into a repository for control and tracking purposes. It is distinct from classification schemes or file references, which organize records according to their function or subject content. The two serve different purposes and may coexist.
Assigning an accession number means the records have been permanently preserved or archived.
Accessioning marks the point of taking materials into custody and establishing control over them. It does not by itself constitute appraisal, arrangement, description, or a decision on permanent preservation. Whether records are ultimately retained permanently, transferred elsewhere, or disposed of depends on subsequent processes and applicable policy.
Each individual document receives its own accession number.
An accession number typically applies to a group of records received together as part of a single transfer or acquisition, rather than to each item. Item-level identification, where needed, is usually handled through separate descriptive or arrangement metadata.

Best practices

Assign accession numbers according to a documented, consistent scheme so that each identifier is unique within the repository and its meaning is unambiguous over time.
Record the accession number alongside supporting metadata about the transfer or acquisition event, such as the source, date of receipt, and extent of materials, to maintain a reliable link between the identifier and the records.
Keep accession numbers stable once assigned, avoiding reuse or reassignment, so that references in registers, finding aids, and audit trails remain reliable.
Distinguish the accession number from classification codes, file references, and later descriptive identifiers in your systems and documentation to prevent conflation of these separate functions.
Treat accessioning as establishing custody and control rather than as a preservation or disposition decision, and ensure that appraisal, description, and disposition steps are documented separately.
Align accession numbering practices with any applicable institutional policy or governing archival guidance, recognizing that specific conventions may vary by organization and jurisdiction.