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The Retrieve Documents service provides a mechanism to retrieve the electronic health information. It is used in conjunction with the Query for Documents service, which returns a list of document references that Retrieve Documents uses to retrieve patient records. The service can be viewed as receiving document requests to which it must respond, and sending outgoing requests in order to retrieve patient health information.

Through the Query for Documents service, an HIE may receive one or more references to documents for patient records that satisfied query parameters for a given patient. The Retrieve Documents service allows an HIE to use that list of references to request individual documents or sets from the list as a single action and allows the responder to securely return the document to the requester and audit the retrieval of the document.
In this context, a "document" refers to the form of electronic health information as it is transferred between NHIEs, not as it is stored in an HIE. Any HIE may store health information in whatever format or repository it chooses so long as the HIE can respond to queries and retrieve document requests. Specifically, a document transferred between NHIEs or systems need not meet the criteria for persistence, stewardship, etc., as identified by the HL7 Structured Documents committee. The primary expected use in the context of the Nationwide Health Information Network is that these documents are formatted as XML data following the HL7 Clinical Document Architecture standard, but nothing precludes this interface from being used to query for other kinds of documents.
NHIEs or systems that generate documents dynamically on demand by aggregating data from multiple sources must ensure that the generated document remains available, unaltered, once a document has been retrieved once. Specifically:

• A document reference may "expire" after a Query for Documents request has been received and responded to if and only if no subsequent Retrieve Documents request has been received and responded to for that document
• For documents that have been shared with another HIE or system via a Retrieve Documents service, the document reference and the document itself must remain available for future Retrieve Documents requests

CONNECT includes services to retrieve documents and respond to requests for documents as well as a reference implementation of the document repository and a document cache that may be used for documents created dynamically on demand.
For incoming messages, an authorized user, such as a provider, uses his or her Nationwide Health Information Network-enabled system to identify documents from those previously returned by a Query for Documents request that are relevant to the patient encounter and for which they are authorized. That system invokes the Retrieve Documents service in its Nationwide Health Information Network gateway, which in turn contacts gateways that contain or provide access to those documents, including CONNECT, requesting the document or documents as attachments. The CONNECT gateway and adapter logical components work together to process the request, including checking policy, authorization of the initiator, and preferences of the patient, and respond with the documents as attachments, if they exist and access is allowed. Those documents are returned to the remote gateway and its associated health system, which may render the documents for viewing, incorporating the information in data repositories on the remote system or otherwise processing the information.
For outgoing messages, the user of the existing health system utilizing CONNECT likewise identifies one or more documents for retrieval, which uses CONNECT to contact NHIE or entity gateways to request documents that exist on those respective systems. Likewise the responses from one or multiple gateways are aggregated by CONNECT and the result provided back to the existing health system where the documents may be rendered for viewing or the data incorporated into the existing system data repositories.
Note that retrieval requests can be sent to multiple gateways on the exchange network.