FAR 4.001—Definitions.
Plain-English Summary
FAR 4.001 defines two core identification terms used throughout FAR Part 4: the Procurement Instrument Identifier (PIID) and the supplementary procurement instrument identifier. The PIID is the Government-unique identifier assigned to each solicitation, contract, agreement, or order, and it is the primary way the Government tracks and distinguishes procurement actions across systems and records. The supplementary procurement instrument identifier is a non-unique identifier used together with the PIID to identify a specific action within that instrument, such as an amendment number tied to a solicitation number. In practice, these definitions support consistent numbering, recordkeeping, reporting, and traceability for procurement actions, including delivery orders, task orders, basic ordering agreements, and amended solicitations. The section also points readers to FAR 4.1602 for additional guidance on PIID structure and use. For contracting personnel and contractors, the practical significance is that correct identifier use affects document control, data quality, auditability, and the ability to match related actions across the acquisition lifecycle.
Key Rules
PIID is government-unique
Each solicitation, contract, agreement, or order must have a Government-unique identifier. This identifier is the primary reference used to distinguish one procurement instrument from another.
PIID covers all procurement instruments
The definition applies broadly to solicitations, contracts, agreements, and orders. Agencies may use the contract number together with an order or agreement number for actions such as delivery orders, task orders, or basic ordering agreements.
Supplementary identifier is non-unique
A supplementary procurement instrument identifier is not unique by itself; it is used only in combination with the PIID. It identifies a specific action or component within the larger procurement instrument.
Amendments use paired numbering
For amended solicitations, the solicitation PIID remains the Government-unique base number, and the amendment number serves as the supplementary identifier. The amendment number alone does not identify the action.
Use with FAR 4.1602
This section works together with FAR 4.1602, which provides additional rules and examples for PIID assignment and format. Users should follow both the definition here and the detailed implementation guidance elsewhere in Part 4.
Responsibilities
Contracting Officer / Contracting Activity
Assign and maintain the correct PIID for each solicitation, contract, agreement, or order, and ensure any supplementary identifier is used only as a companion to the PIID. The contracting office must keep numbering consistent across amendments, orders, and related procurement records.
Agency
Establish and apply PIID practices that ensure identifiers are unique, traceable, and compatible with agency systems and reporting requirements. Agencies must also align their numbering practices with FAR Part 4 and related guidance.
Contractor
Use the PIID and any supplementary identifier exactly as provided in Government documents and correspondence. Contractors should not create, alter, or substitute identifiers when referencing solicitations, contracts, orders, or amendments.
Acquisition/Contract Administration Personnel
Verify that procurement records, modifications, amendments, and order documents carry the correct identifier structure and that related actions can be matched accurately in files and systems.
Practical Implications
Correct numbering is essential for file integrity, e-commerce systems, reporting, and audit trails; a wrong PIID can cause mismatched records or lost actions.
A supplementary identifier by itself is not enough to identify a procurement action, so users must always pair it with the base PIID.
Amendments, orders, and related actions should be tracked consistently to avoid confusion between the original instrument and later changes.
Contractors should rely on the Government-provided identifier exactly as written, especially when submitting invoices, correspondence, or performance documentation.
When in doubt, check the PIID format and related numbering rules in FAR 4.1602 and agency supplements before issuing or using a document number.
Official Regulatory Text
As used in this part- Procurement Instrument Identifier (PIID) means the Government-unique identifier for each solicitation, contract, agreement, or order. For example, an agency may use as its PIID for procurement actions, such as delivery and task orders or basic ordering agreements, the order or agreement number in conjunction with the contract number (see 4.1602 ). Supplementary procurement instrument identifier means the non-unique identifier for a procurement action that is used in conjunction with the Government-unique identifier. For example, an agency may use as its PIID for an amended solicitation, the Government-unique identifier for a solicitation number ( e.g. , N0002309R0009) in conjunction with a non-unique amendment number ( e.g. , 0001). The non-unique amendment number represents the supplementary PIID.