diff --git a/SUMMARY.md b/SUMMARY.md
index 91ffd24..3fd086c 100644
--- a/SUMMARY.md
+++ b/SUMMARY.md
@@ -12,6 +12,7 @@
   * [MPF Pipeline](run-payerbox/provider-directory-pipeline.md)
   * [Maintain](run-payerbox/maintain/README.md)
     * [Observability](run-payerbox/maintain/observability.md)
+    * [Event Notifications](run-payerbox/maintain/event-notifications.md)
     * [Upgrade](run-payerbox/maintain/upgrade.md)
 * [Interop APIs](interop-apis/README.md)
   * [Patient Access](interop-apis/patient-access.md)
diff --git a/docs/run-payerbox/maintain/README.md b/docs/run-payerbox/maintain/README.md
index 231eaa3..3adb4d4 100644
--- a/docs/run-payerbox/maintain/README.md
+++ b/docs/run-payerbox/maintain/README.md
@@ -5,4 +5,5 @@ Day-2 operations for a running Payerbox deployment.
 | Page | What it covers |
 |---|---|
 | [Observability](observability.md) | Prometheus metrics, BALP audit logs, runbooks |
+| [Event Notifications](event-notifications.md) | Push FHIR events to AWS SNS or webhooks via topic-based subscriptions |
 | [Upgrade](upgrade.md) | Bundle and per-image upgrade, breaking changes, rollback |
diff --git a/docs/run-payerbox/maintain/event-notifications.md b/docs/run-payerbox/maintain/event-notifications.md
new file mode 100644
index 0000000..5d5cc35
--- /dev/null
+++ b/docs/run-payerbox/maintain/event-notifications.md
@@ -0,0 +1,234 @@
+# Event Notifications
+
+Payerbox can push FHIR resource events to external systems as they happen — for example, notifying a downstream system the moment a prior-authorization decision is recorded. This is built on Aidbox **topic-based subscriptions** and is configured entirely through FHIR resources.
+
+This page is an operator how-to: how to define what to notify on, where to send it, and how to keep that configuration healthy.
+
+## How it works
+
+Two resources work together:
+
+| Resource | Role |
+|---|---|
+| `AidboxSubscriptionTopic` | The trigger — which resource type, an optional FHIRPath criterion, and which interactions (create / update / delete) fire it. |
+| `AidboxTopicDestination` | The sink — where matching events go. Its `kind` selects the transport (AWS SNS or HTTP webhook); `content` controls the payload shape. |
+
+When a CRUD operation matches a topic's trigger, the engine writes one event per bound destination. Senders drain those events asynchronously, so a slow or unavailable subscriber never blocks the originating FHIR write.
+
+```mermaid
+flowchart LR
+  write(FHIR write<br/>create / update / delete):::violet2
+  topic(AidboxSubscriptionTopic<br/>trigger + FHIRPath):::violet2
+  dest(AidboxTopicDestination<br/>SNS or webhook):::violet2
+  ext(External system<br/>SNS topic / HTTP endpoint):::yellow2
+
+  write --> topic --> dest --> ext
+```
+
+### Delivery guarantees
+
+Two delivery modes are available, selected by the destination `kind`:
+
+- **At-least-once** — events are persisted to a database queue and retried until acknowledged. A subscriber may see the same event more than once, so handlers must be idempotent. Use this for anything where a missed notification matters (claim and decision notifications).
+- **Best-effort** — fire-and-forget. Lower latency, no retry. Use only where an occasional drop is acceptable.
+
+## Destination kinds
+
+| `kind` | Transport | Profile (`meta.profile`) |
+|---|---|---|
+| `webhook-at-least-once` | HTTP POST to an endpoint | `http://aidbox.app/StructureDefinition/aidboxtopicdestination-webhook-at-least-once` |
+| `aws-sns-at-least-once` | AWS SNS, queued + retried | `http://aidbox.app/StructureDefinition/aidboxtopicdestination-aws-sns-at-least-once` |
+| `aws-sns-best-effort` | AWS SNS, fire-and-forget | `http://aidbox.app/StructureDefinition/aidboxtopicdestination-aws-sns-best-effort` |
+| `custom-aws-sns-at-least-once` | AWS SNS, queued + retried, with reference enrichment | `http://health-samurai.io/fhir/core/StructureDefinition/aidboxtopicdestination-customAWSSNSAtLeastOnceProfile` |
+| `custom-aws-sns-best-effort` | AWS SNS, fire-and-forget, with reference enrichment | `http://health-samurai.io/fhir/core/StructureDefinition/aidboxtopicdestination-customAWSSNSBestEffortProfile` |
+
+The `custom-aws-sns-*` kinds are a Payerbox extension of the AWS SNS senders. When the `aidboxUrl` and `aidboxAuth` parameters are set, the sender resolves the triggering resource's references and ships an enriched payload instead of the bare resource; without those parameters they behave exactly like the plain `aws-sns-*` kinds.
+
+The `webhook-at-least-once` kind and the plain `aws-sns-*` kinds are shipped by Aidbox and are accepted out of the box. The `custom-aws-sns-*` kinds use Payerbox-specific profiles that must be whitelisted before use — see Step 1 below.
+
+## Configure a notification
+
+{% stepper %}
+{% step %}
+### Whitelist the destination profile (custom SNS kinds only)
+
+`AidboxTopicDestination` is constrained by an `allow-destinations` rule that lists the accepted `meta.profile` URLs. Built-in kinds (`webhook-at-least-once`, `aws-sns-*`) are already on this list. The Payerbox `custom-aws-sns-*` profiles are not, so they must be added **before** any destination that uses them is created — otherwise the destination is rejected at creation.
+
+Patch the constraint to include the custom profile URLs:
+
+{% code title="patch-allow-destinations.json" %}
+```json
+{
+  "resourceType": "Parameters",
+  "parameter": [
+    {
+      "name": "operation",
+      "part": [
+        {"name": "type", "valueCode": "add"},
+        {"name": "path", "valueString": "differential.element.where(id='AidboxTopicDestination.meta.profile').binding.extension.valueSet"},
+        {"name": "value", "valueUri": "http://health-samurai.io/fhir/core/StructureDefinition/aidboxtopicdestination-customAWSSNSAtLeastOnceProfile"}
+      ]
+    }
+  ]
+}
+```
+{% endcode %}
+
+```bash
+curl -sS -u "$ROOT_CLIENT" \
+  -H "Content-Type: application/json" \
+  -X PATCH "$AIDBOX_URL/fhir/StructureDefinition/AidboxTopicDestination" \
+  -d @patch-allow-destinations.json
+```
+
+Repeat with the `customAWSSNSBestEffortProfile` URL if you use the best-effort variant. The list is additive — each PATCH appends one profile.
+{% endstep %}
+
+{% step %}
+### Define the subscription topic
+
+Declare what to notify on. The `trigger.fhirPathCriteria` narrows the firing condition; omit it to fire on every interaction of the resource type.
+
+{% code title="subscription-topic.json" %}
+```json
+{
+  "resourceType": "AidboxSubscriptionTopic",
+  "id": "pas-claimresponse-status",
+  "url": "http://prior-auth.example.org/SubscriptionTopic/pas-claimresponse-status",
+  "status": "active",
+  "description": "Notify when PAS ClaimResponses are created or updated",
+  "trigger": [
+    {"resource": "ClaimResponse", "fhirPathCriteria": "use = 'preauthorization'"}
+  ]
+}
+```
+{% endcode %}
+
+```bash
+curl -sS -u "$ROOT_CLIENT" \
+  -H "Content-Type: application/json" \
+  -X PUT "$AIDBOX_URL/AidboxSubscriptionTopic/pas-claimresponse-status" \
+  -d @subscription-topic.json
+```
+{% endstep %}
+
+{% step %}
+### Create the topic destination
+
+Bind a destination to the topic's `url`. Pick the tab that matches your transport.
+
+{% tabs %}
+{% tab title="AWS SNS" %}
+{% code title="topic-destination-sns.json" %}
+```json
+{
+  "resourceType": "AidboxTopicDestination",
+  "id": "pas-claimresponse-sns",
+  "kind": "custom-aws-sns-at-least-once",
+  "meta": {
+    "profile": ["http://health-samurai.io/fhir/core/StructureDefinition/aidboxtopicdestination-customAWSSNSAtLeastOnceProfile"]
+  },
+  "status": "active",
+  "topic": "http://prior-auth.example.org/SubscriptionTopic/pas-claimresponse-status",
+  "parameter": [
+    {"name": "topicArn", "valueString": "arn:aws:sns:us-east-1:123456789012:pas-claimresponse"},
+    {"name": "region", "valueString": "us-east-1"},
+    {"name": "batchSize", "valueInteger": 1}
+  ],
+  "content": "full-resource"
+}
+```
+{% endcode %}
+
+SNS parameters:
+
+| Parameter | Required | Notes |
+|---|---|---|
+| `topicArn` | Yes | Target SNS topic ARN. For a FIFO topic (ARN ends in `.fifo`), also set `messageGroupId`. |
+| `region` | Yes | AWS region, e.g. `us-east-1`. |
+| `accessKeyId` / `secretAccessKey` | No | Explicit credentials. If omitted, the default AWS credential chain is used (IAM role, environment, etc.). `secretAccessKey` is required when `accessKeyId` is set. |
+| `endpointOverride` | No | Alternate SNS endpoint URL — used for local testing against an SNS emulator. |
+| `messageGroupId` | FIFO only | Required when the topic ARN ends in `.fifo`. |
+| `batchSize` | No | At-least-once only; 1–10. Number of events published per batch. |
+| `aidboxUrl` / `aidboxAuth` | No | `custom-aws-sns-*` kinds only. Set both to enable reference enrichment; `aidboxAuth` is `username:password` for Basic auth. |
+
+Prefer the default credential chain (IAM role) in production and avoid putting long-lived `secretAccessKey` values in the destination resource.
+{% endtab %}
+
+{% tab title="HTTP webhook" %}
+{% code title="topic-destination-webhook.json" %}
+```json
+{
+  "resourceType": "AidboxTopicDestination",
+  "id": "pas-claimresponse-webhook",
+  "kind": "webhook-at-least-once",
+  "meta": {
+    "profile": ["http://aidbox.app/StructureDefinition/aidboxtopicdestination-webhook-at-least-once"]
+  },
+  "status": "active",
+  "topic": "http://prior-auth.example.org/SubscriptionTopic/pas-claimresponse-status",
+  "parameter": [
+    {"name": "endpoint", "valueUrl": "https://downstream.example.org/webhooks/claimresponse"},
+    {"name": "timeout", "valueUnsignedInt": 5000}
+  ],
+  "content": "full-resource"
+}
+```
+{% endcode %}
+
+Webhook parameters: `endpoint` (target URL, required) and `timeout` (per-delivery timeout in milliseconds). If the endpoint requires Basic auth, configure the corresponding Aidbox client with `grant_types: ["basic"]`.
+{% endtab %}
+{% endtabs %}
+
+```bash
+curl -sS -u "$ROOT_CLIENT" \
+  -H "Content-Type: application/json" \
+  -X PUT "$AIDBOX_URL/AidboxTopicDestination/pas-claimresponse-sns" \
+  -d @topic-destination-sns.json
+```
+
+`content: "full-resource"` ships the complete triggering resource in the notification. With a `custom-aws-sns-*` kind and `aidboxUrl`/`aidboxAuth` set, the payload additionally carries the resolved referenced resources.
+{% endstep %}
+
+{% step %}
+### Verify
+
+Trigger a matching write and confirm delivery downstream — for SNS, watch the topic's `NumberOfMessagesPublished` metric; for a webhook, check the receiver's logs. Do not rely on the internal event queue to confirm activity: the at-least-once queue is drained and the row deleted on successful delivery, so a healthy pipeline shows an empty queue within seconds.
+{% endstep %}
+{% endstepper %}
+
+## Provisioning at deploy time
+
+In production these resources are typically created from an init-bundle rather than by hand, with environment-variable substitution for environment-specific values (topic ARN, region, credentials). Two ordering rules apply:
+
+- The `allow-destinations` whitelist PATCH must come **before** any destination that uses a custom profile.
+- A subscription topic should exist before the destinations that reference its `url`.
+
+## Updating a destination
+
+`AidboxTopicDestination` resources are **immutable** — Aidbox rejects `PUT` and `PATCH` on an existing destination. To change one (a new ARN, a different endpoint), **delete and re-create** it:
+
+```bash
+curl -sS -u "$ROOT_CLIENT" -X DELETE "$AIDBOX_URL/AidboxTopicDestination/pas-claimresponse-sns"
+# then re-create with the new configuration (Step 3)
+```
+
+Re-creation is also what registers the destination with the in-memory delivery engine. A destination that exists in the database but was never created against a running engine (for example, an init-bundle entry that was a no-op because the resource already existed) will not deliver events. If a topic stops firing after a restart, delete and re-create the destination to force re-registration.
+
+## Gotchas
+
+- **Handlers must be idempotent.** At-least-once delivery can repeat an event. Deduplicate on the resource id and version, or guard with your own idempotency key.
+- **Updates re-fire.** The engine fires on every interaction matching the criterion, including writes your own subscriber makes back into Aidbox. Avoid feedback loops when subscribing to a resource your downstream also updates.
+- **Stale configuration does not self-correct.** Because destinations are immutable and init-bundles commonly create them only when absent, a wrong value set at first boot persists silently. Re-create the destination to fix it.
+
+## Current limitations
+
+- Destinations cannot be edited in place — every change is delete-and-re-create.
+- There is no built-in dead-letter queue; an at-least-once event retries until delivered.
+- Reference enrichment is available only on the `custom-aws-sns-*` kinds, not on webhooks.
+
+## Related
+
+- [Observability](observability.md) — metrics and audit logs for a running deployment
+- [Architecture](../architecture.md) — where notifications fit in the component view
+- [PAS](../../prior-auth/pas.md) — the prior-authorization flow that drives most notifications