diff --git a/projects/cas2-and-delius/README.md b/projects/cas2-and-delius/README.md
index f5fc098a1d..9694c18027 100644
--- a/projects/cas2-and-delius/README.md
+++ b/projects/cas2-and-delius/README.md
@@ -1,3 +1,47 @@
-# cas2-and-delius
+# CAS2 and Delius
-// TODO Describe the service
\ No newline at end of file
+Service that responds to Community Accommodation Services Tier 2 (CAS2) domain events. The service is responsible for updating Delius with progress of referrals to short-term accommodation for people released from custody on Home Detention Curfew or bail.
+
+## Business Need
+
+Ensuring the Probation Practitioner has an up-to-date view of activity in the CAS2 service when interacting with the probation case via Delius.
+
+## Context Map
+
+
+
+## Workflows
+
+CAS2 domain events are raised in real time as referral applications are processed. There is a single update domain event to inform of progress or changes to the referral application.
+
+### Create a CAS2 Referral Application
+
+A referral application is created in the CAS2 service which is reflected in a Delius contact. An `EXTERNAL_REFERENCE` URN is added to the contact in the form `urn:hmpps:cas2:application-submitted:{referralId}` using the CAS2 referral ID as a unique reference.
+
+| Business Event | Message Event Type / Filter |
+|---------------------------------------------------------------|----------------------------------------------|
+| Submission of a accommodation referral application | applications.cas2.application.submitted |
+
+
+
+### Update the Status of a CAS2 Referral Application
+
+A referral application is updated in the CAS2 service which is reflected in a Delius contact. Only a single update contact exists in Delius for any single CAS2 referral and the contact is updated with the latest status. An `EXTERNAL_REFERENCE` URN is added to the contact in the form `urn:hmpps:cas2:application-status-updated:{referralId}` using the CAS2 referral ID as a unique reference.
+
+| Business Event | Message Event Type / Filter |
+|---------------------------------------------------------------|----------------------------------------------|
+| Update to the status of an accommodation referral application | applications.cas2.application.status-updated |
+
+
+
+## Interfaces
+
+### Message Interface
+
+The service responds to HMPPS Domain Event messages via the
+[Queue](https://github.com/ministryofjustice/cloud-platform-environments/blob/main/namespaces/live.cloud-platform.service.justice.gov.uk/hmpps-probation-integration-services-prod/resources/cas2-and-delius-queue.tf).
+The events are raised by the [HMPPS Approved Premises API](https://github.com/ministryofjustice/hmpps-approved-premises-api/) which handles backend integration for the [CAS2 UI](https://github.com/ministryofjustice/hmpps-community-accommodation-tier-2-ui)
+
+Example [messages](./src/dev/resources/messages/) are in the development source tree.
+
+Incoming messages are filtered on `eventType` by the [SQS queue policy](https://github.com/ministryofjustice/cloud-platform-environments/blob/2aeb8aeb7b7798cbe12bc81b14d01aaa707041f1/namespaces/live.cloud-platform.service.justice.gov.uk/hmpps-probation-integration-services-prod/resources/cas2-and-delius-queue.tf#L5-L10)
diff --git a/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-context-map.d2 b/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-context-map.d2
new file mode 100644
index 0000000000..792eb45a49
--- /dev/null
+++ b/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-context-map.d2
@@ -0,0 +1,28 @@
+
+style { ...@../../../../script/style.style }
+vars { ...@../../../../script/style.vars }
+** { ...@../../../../script/style.all-style }
+
+context-cas2: CAS2 Context {
+ entities: Entities {
+ grid-columns: 2
+ pop: Person on Probation
+ referral: Accommodation Referral
+ }
+}
+
+context-delius: Delius Context {
+
+ interface: CAS2 and Delius {
+ type: Anti-Corruption\nLayer
+ }
+
+ entities: Entities {
+ grid-columns: 2
+ pop: Person on Probation
+ contact: Contact
+ manager: Offender Manager
+ }
+}
+
+context-cas2--context-delius.interface: Upstream\n\n\nDownstream
diff --git a/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-workflow-application-update.d2 b/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-workflow-application-update.d2
new file mode 100644
index 0000000000..2082c48ac4
--- /dev/null
+++ b/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-workflow-application-update.d2
@@ -0,0 +1,42 @@
+# CAS2 Workflow: Referral Application Status Update
+
+style { ...@../../../../script/style.style }
+vars { ...@../../../../script/style.vars }
+** { ...@../../../../script/style.all-style }
+
+direction: right
+
+# What triggers the workflow?
+cas2: CAS2 {
+ style.font-size: 24
+
+ explanation: |md
+ ## Referral Application Workflow
+ Updates to referral applications raise domain events
+ |
+
+ application_updated: Application Updated
+}
+
+domain_event_1: "applications.cas2\n.application.status-updated" {
+ style.font-size: 12
+ shape: queue
+}
+
+# What happens in Delius?
+delius: Delius {
+ style.font-size: 24
+
+ explanation: |md
+ ## Delius Workflow
+ Referral application status contact is created\
+ or updated Delius to reflect referral application changes
+ |
+
+ d_contact_create: Create Contact
+ d_contact_update: Update Contact
+}
+
+cas2 -> domain_event_1
+
+domain_event_1 -> delius
diff --git a/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-workflow-application.d2 b/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-workflow-application.d2
new file mode 100644
index 0000000000..9cca491b38
--- /dev/null
+++ b/projects/cas2-and-delius/tech-docs/diag/cas2-and-delius-workflow-application.d2
@@ -0,0 +1,41 @@
+# CAS2 Workflow: Referral Application
+
+style { ...@../../../../script/style.style }
+vars { ...@../../../../script/style.vars }
+** { ...@../../../../script/style.all-style }
+
+direction: right
+
+# What triggers the workflow?
+cas2: CAS2 {
+ style.font-size: 24
+
+ explanation: |md
+ ## Referral Application Workflow
+ Referral application actions raise domain events
+ |
+
+ application_submitted: Application Submitted
+}
+
+domain_event_1: "applications.cas2\n.application.submitted" {
+ style.font-size: 12
+ shape: queue
+}
+
+# What happens in Delius?
+delius: Delius {
+ style.font-size: 24
+
+ explanation: |md
+ ## Delius Workflow
+ Contact is added to Delius \
+ to indicate referral application creation
+ |
+
+ d_contact: Create Contact
+}
+
+cas2 -> domain_event_1
+
+domain_event_1 -> delius
diff --git a/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-context-map.svg b/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-context-map.svg
new file mode 100644
index 0000000000..8f83541c80
--- /dev/null
+++ b/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-context-map.svg
@@ -0,0 +1,120 @@
+
diff --git a/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-workflow-application-update.svg b/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-workflow-application-update.svg
new file mode 100644
index 0000000000..5698de4da6
--- /dev/null
+++ b/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-workflow-application-update.svg
@@ -0,0 +1,854 @@
+
diff --git a/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-workflow-application.svg b/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-workflow-application.svg
new file mode 100644
index 0000000000..ff3edef46f
--- /dev/null
+++ b/projects/cas2-and-delius/tech-docs/source/img/cas2-and-delius-workflow-application.svg
@@ -0,0 +1,853 @@
+
diff --git a/projects/external-api-and-delius/src/main/kotlin/uk/gov/justice/digital/hmpps/model/Registration.kt b/projects/external-api-and-delius/src/main/kotlin/uk/gov/justice/digital/hmpps/model/Registration.kt
index 5f23e62b8f..9f3cc15061 100644
--- a/projects/external-api-and-delius/src/main/kotlin/uk/gov/justice/digital/hmpps/model/Registration.kt
+++ b/projects/external-api-and-delius/src/main/kotlin/uk/gov/justice/digital/hmpps/model/Registration.kt
@@ -1,9 +1,12 @@
package uk.gov.justice.digital.hmpps.model
+import io.swagger.v3.oas.annotations.media.Schema
import java.time.LocalDate
data class Registration(
+ @Schema(example = "RCCO")
val code: String,
+ @Schema(example = "Child Concerns")
val description: String,
val startDate: LocalDate,
val reviewDate: LocalDate?,
diff --git a/script/style.d2 b/script/style.d2
new file mode 100644
index 0000000000..1d94a61d05
--- /dev/null
+++ b/script/style.d2
@@ -0,0 +1,21 @@
+style {
+ fill: "#ffffff"
+ stroke: "#000000"
+ stroke-width: 2
+}
+
+all-style {
+ style {
+ border-radius: 10
+ stroke-width: 2
+ }
+}
+
+vars: {
+ d2-config: {
+ pad: 25
+ center: true
+ layout-engine: elk
+ theme-id: 8
+ }
+}