diff --git a/README.md b/README.md
index 16d03d6..137c609 100644
--- a/README.md
+++ b/README.md
@@ -444,6 +444,25 @@ high-water mark — the highest `severity` label any of its alerts has carried 
 an incident that hit `critical` still reads as critical after the critical alert
 clears.
 
+### Several clusters, one team
+
+A team with one Alertmanager per Kubernetes cluster, each posting to its own
+source, needs two settings or the clusters run together.
+
+1. Give every alert a `cluster` label at the source. In Prometheus that is
+   `externalLabels: {cluster: prod-eu}` (kube-prometheus-stack:
+   `prometheus.prometheusSpec.externalLabels`).
+2. Add `cluster` to `group_by` in `alertmanager.yml`.
+
+The second one is the one that matters. Incidents are matched on the team and
+Alertmanager's `groupKey`, and the `groupKey` does not include external labels:
+without `cluster` in `group_by`, the same alert in two clusters has the same
+key and joins one incident. With it, each cluster gets its own, `cluster` is in
+the incident's `group_labels`, and the web UI shows it as a coloured chip on the
+queue, the incident and the alert list, instead of leaving it in the title.
+An alert that is not grouped by `cluster` still shows the chip on the alert
+list, which reads the label from the alert itself.
+
 ### An incident opens only on a new occurrence
 
 An incident opens when an alert **transitions into firing**: a fingerprint that
diff --git a/internal/web/static/app.css b/internal/web/static/app.css
index 53da2f8..679df47 100644
--- a/internal/web/static/app.css
+++ b/internal/web/static/app.css
@@ -488,7 +488,15 @@ input:focus, textarea:focus { outline: none; border-color: var(--accent); box-sh
 }
 .badge::before { content: ""; width: 7px; height: 7px; border-radius: 50%; background: currentColor; }
 .badge.plain::before { display: none; }
-.badge .badge-icon { width: 12px; height: 12px; stroke-width: 2.4; }
+.badge .badge-icon, .origin-chip .badge-icon { width: 12px; height: 12px; stroke-width: 2.4; }
+/* The cluster an incident or alert came from. Same shape as a badge, coloured
+   from the rcN palette (see originClass in format.js), never the severity one. */
+.origin-chip {
+  display: inline-flex; align-items: center; gap: 5px; max-width: 100%;
+  padding: 1px 8px; border-radius: 999px;
+  font-size: 12px; font-weight: 700; letter-spacing: 0.01em; white-space: nowrap;
+  overflow: hidden; text-overflow: ellipsis;
+}
 .badge.st-triggered, .badge.st-firing { background: var(--crit-soft); color: var(--crit); }
 .badge.st-acknowledged { background: var(--warn-soft); color: var(--warn); }
 .badge.st-snoozed { background: var(--snooze-soft); color: var(--snooze); }
diff --git a/internal/web/static/js/alerts.js b/internal/web/static/js/alerts.js
index 28fd585..92fe385 100644
--- a/internal/web/static/js/alerts.js
+++ b/internal/web/static/js/alerts.js
@@ -2,8 +2,8 @@
 // incident it belongs to, which is where anything can be done about it.
 
 import * as api from './api.js';
-import { h, clear, badge, severityBadge, emptyState, spinner } from './ui.js';
-import { age, labelSummary } from './format.js';
+import { h, clear, badge, severityBadge, originChip, emptyState, spinner } from './ui.js';
+import { age, labelSummary, originOf, ORIGIN_LABEL } from './format.js';
 
 const FILTERS = [
   { id: 'firing', label: 'Firing', query: { status: 'firing' } },
@@ -77,7 +77,8 @@ function row(a) {
   const summary = (a.annotations && a.annotations.summary) || '';
   const sev = a.labels && a.labels.severity;
   const labels = labelSummary(Object.fromEntries(
-    Object.entries(a.labels || {}).filter(([k]) => k !== 'severity')));
+    Object.entries(a.labels || {}).filter(([k]) => k !== 'severity' && k !== ORIGIN_LABEL)));
+  const origin = originOf(a.labels);
   const linked = a.incident_id != null;
   return h(linked ? 'a' : 'div', {
     class: `row st-${a.status} ${linked ? '' : 'no-link'}`,
@@ -86,6 +87,7 @@ function row(a) {
     h('div', { class: 'row-title', text: a.name }),
     h('div', { class: 'row-age', title: a.starts_at, text: age(a.status === 'firing' ? a.starts_at : a.received_at) }),
     h('div', { class: 'row-meta' },
+      origin && originChip(origin),
       badge(a.status === 'firing' ? 'Firing' : 'Resolved', `st-${a.status}`),
       sev && severityBadge(sev),
       summary && h('span', { text: summary }),
diff --git a/internal/web/static/js/format.js b/internal/web/static/js/format.js
index 49ed148..9bf994f 100644
--- a/internal/web/static/js/format.js
+++ b/internal/web/static/js/format.js
@@ -117,3 +117,36 @@ export function labelSummary(labels, skip = 'alertname') {
 export function initial(name) {
   return (name || '?').trim().charAt(0) || '?';
 }
+
+// Where an incident or alert came from, for a team with several Kubernetes
+// clusters (or other origins) behind it: the value of one label, `cluster` by
+// convention. It comes from Prometheus's externalLabels, so it is on every
+// alert; an incident carries it only when it is in Alertmanager's group_by,
+// which is also what keeps two clusters' identical alerts from merging into one
+// incident (see the README, "Several clusters, one team").
+export const ORIGIN_LABEL = 'cluster';
+
+export function originOf(labels) {
+  const v = labels && labels[ORIGIN_LABEL];
+  return v ? String(v) : null;
+}
+
+// A stable colour for an origin, from the six-colour rcN palette app.css has,
+// so "prod-eu" is the same colour on every row without anything being stored.
+export function originClass(value) {
+  let n = 0;
+  for (const ch of value) n = (n * 31 + ch.charCodeAt(0)) >>> 0;
+  return `rc${(n % 6) + 1}`;
+}
+
+// The title without its `cluster=...` part, for a row that shows the origin as
+// a chip: the server puts every grouping label in the title, so the cluster
+// would otherwise appear twice. Anything that does not look like the server's
+// "name (k=v, k=v)" shape is returned unchanged.
+export function titleWithoutOrigin(title, value) {
+  if (!value) return title;
+  const m = title.match(/^(.*?) \((.*)\)$/s);
+  if (!m) return title;
+  const rest = m[2].split(', ').filter((p) => p !== `${ORIGIN_LABEL}=${value}`);
+  return rest.length ? `${m[1]} (${rest.join(', ')})` : m[1];
+}
diff --git a/internal/web/static/js/incident.js b/internal/web/static/js/incident.js
index 0b63648..143d6b8 100644
--- a/internal/web/static/js/incident.js
+++ b/internal/web/static/js/incident.js
@@ -4,10 +4,10 @@
 import * as api from './api.js';
 import * as poll from './poll.js';
 import {
-  h, clear, icon, badge, severityBadge, labelChip, openSheet, closeSheet, confirm, toast, spinner, emptyState,
+  h, clear, icon, badge, severityBadge, originChip, labelChip, openSheet, closeSheet, confirm, toast, spinner, emptyState,
 } from './ui.js';
 import {
-  ago, when, until, duration, isFuture, STATUS_LABEL,
+  ago, when, until, duration, isFuture, originOf, STATUS_LABEL,
 } from './format.js';
 import { myID, users } from './state.js';
 import { back } from './app.js';
@@ -99,6 +99,8 @@ function render() {
 
 function statusBadges() {
   const out = [];
+  const origin = originOf(inc.group_labels);
+  if (origin) out.push(originChip(origin));
   if (inc.severity) out.push(severityBadge(inc.severity));
   out.push(badge(STATUS_LABEL[inc.status] || inc.status, `st-${inc.status}`));
   if (inc.status !== 'resolved' && isFuture(inc.snoozed_until)) {
diff --git a/internal/web/static/js/queue.js b/internal/web/static/js/queue.js
index 111f718..b2b12c7 100644
--- a/internal/web/static/js/queue.js
+++ b/internal/web/static/js/queue.js
@@ -1,8 +1,8 @@
 // The incident queue: filter chips and a list of incident rows.
 
 import * as api from './api.js';
-import { h, clear, badge, severityBadge, emptyState, spinner, fadeOnOverflow } from './ui.js';
-import { ago, until, isFuture, severityClass, labelSummary } from './format.js';
+import { h, clear, badge, severityBadge, originChip, emptyState, spinner, fadeOnOverflow } from './ui.js';
+import { ago, until, isFuture, severityClass, labelSummary, originOf, titleWithoutOrigin } from './format.js';
 import { state, myID, onTeamChange } from './state.js';
 import * as onboarding from './onboarding.js';
 import { navigate } from './app.js';
@@ -201,15 +201,18 @@ function row(inc, index) {
     ? h('span', { class: 'row-team', text: inc.team_name })
     : null;
 
+  const origin = originOf(inc.group_labels);
+
   return h('a', {
     class: `row ${severityClass(inc.severity)} ${resolved ? 'resolved' : ''} ${index === cursor ? 'kbd-focus' : ''}`,
     href: `/incidents/${inc.id}`,
     'aria-current': inc.id === selected ? 'true' : null,
     dataset: { index: String(index) },
   },
-    h('div', { class: 'row-title', text: inc.title }),
+    h('div', { class: 'row-title', text: titleWithoutOrigin(inc.title, origin) }),
     h('div', { class: 'row-age', title: inc.triggered_at, text: `Triggered ${ago(inc.triggered_at)}` }),
     h('div', { class: 'row-meta' },
+      origin && originChip(origin),
       !impliedStatus && status,
       // The left-border colour alone doesn't say what it means; spell it out
       // too, same badge the incident detail page uses for severity.
diff --git a/internal/web/static/js/ui.js b/internal/web/static/js/ui.js
index 6b771b5..04fe645 100644
--- a/internal/web/static/js/ui.js
+++ b/internal/web/static/js/ui.js
@@ -1,6 +1,6 @@
 // DOM helpers, the bottom sheet, confirmation and toasts.
 
-import { severityClass } from './format.js';
+import { severityClass, originClass } from './format.js';
 
 // h builds an element. attrs: class, text, on<event>, dataset, aria/other
 // attributes; boolean true sets an empty attribute, false/null skips it.
@@ -49,6 +49,7 @@ export function fadeOnOverflow(el) {
 
 // Stroke icons, 24×24. Built as SVG nodes so the CSP needs no inline anything.
 const ICONS = {
+  server: ['rect:3,4,18,6,2', 'rect:3,14,18,6,2', 'M7 7h.01', 'M7 17h.01'],
   alertTriangle: ['M12 4l9.5 16.5h-19z', 'M12 10v4.5', 'M12 17.5h.01'],
   alertCircle: ['circle:12,12,9', 'M12 7.5v5', 'M12 16h.01'],
   infoCircle: ['circle:12,12,9', 'M12 11v5.5', 'M12 7.5h.01'],
@@ -193,6 +194,13 @@ export function badge(text, cls = '') {
   return h('span', { class: `badge ${cls}`, text });
 }
 
+// Where it came from (the cluster): a chip in that origin's colour, with a
+// server icon so it reads as a place and not as a status.
+export function originChip(value) {
+  return h('span', { class: `origin-chip ${originClass(value)}`, title: `Origin: ${value}` },
+    icon('server', 'icon badge-icon'), value);
+}
+
 // The severity as a badge with a shape as well as a colour: a triangle for
 // critical, a circle with ! for warning, a circle with i for anything else, so
 // the coloured bar and badge are not the only thing that says it.