| identifier | No | Identifier[] | Unique identifier |
| instantiatesCanonical | No | canonical[] | Instantiates FHIR protocol or definition |
| instantiatesUri | No | uri[] | Instantiates external protocol or definition |
| basedOn | No | Reference<Resource>[] | Request fulfilled by this communication |
| partOf | No | Reference<Resource>[] | Part of this action |
| inResponseTo | No | Reference<Communication>[] | Reply to |
| status | Yes | code | preparation / in-progress / not-done / on-hold / stopped / completed / entered-in-error / unknown |
| statusReason | No | CodeableConcept | Reason for current status |
| category | No | CodeableConcept[] | Message category |
| priority | No | code | routine / urgent / asap / stat |
| medium | No | CodeableConcept[] | A channel of communication |
| subject | No | Reference<Patient / Group> | Focus of message |
| topic | No | CodeableConcept | Description of the purpose/content |
| about | No | Reference<Resource>[] | Resources that pertain to this communication |
| encounter | No | Reference<Encounter> | Encounter created as part of |
| sent | No | dateTime | When sent |
| received | No | dateTime | When received |
| recipient | No | Reference<Device / Organization / Patient / Practitioner / PractitionerRole / RelatedPerson / Group / CareTeam / HealthcareService>[] | Message recipient |
| sender | No | Reference<Device / Organization / Patient / Practitioner / PractitionerRole / RelatedPerson / HealthcareService> | Message sender |
| reasonCode | No | CodeableConcept[] | Indication for message |
| reasonReference | No | Reference<Condition / Observation / DiagnosticReport / DocumentReference>[] | Why was communication done? |
| payload | No | CommunicationPayload | Message payload |
| - id | No | string | Unique id for inter-element referencing |
| - extension | No | Extension[] | Additional content defined by implementations |
| - modifierExtension | No | Extension[] | Extensions that cannot be ignored even if unrecognized |
| - content[x] | Yes | string, Attachment, Reference<Resource> | Message part content |
| note | No | Annotation[] | Comments made about the communication |
