Agency (originating, transcribing, or modifying):

The originating agency (or source) is the name of the agency (usually a library) that creates an original MARC record.

A transcribing agency is an agency which transcribes a record found in another format, for example, a Library of Congress catalog card, into machine-readable format (a MARC format record).

A modifying agency is an agency which modifies an original MARC format record (other than adding the agency's own holdings data).