diff --git a/src/api/index.js b/src/api/index.js
index 69245c1..3d7fa8f 100644
--- a/src/api/index.js
+++ b/src/api/index.js
@@ -557,7 +557,9 @@ export const supplier = {
 
 /**
  * Company-scoped goods receipts (manifest type = delivery).
- * DeliverySummary = { id, number, type: 'delivery', supplierId, date }
+ * DeliverySummary = { id, number, externalNumber, type: 'delivery', supplierId, date }
+ *   - number: server-allocated, read-only manifest number (from nextNumber('delivery')).
+ *   - externalNumber: user-entered reference (nullable).
  * DeliveryLine = { id, articleId, sku, amount, net, transactedAmount, rebate, tax, comment }
  * Delivery = DeliverySummary & { lines: DeliveryLine[] }
  * DeliveryLineInput = { sku, amount, net, tax, rebate?, transactedAmount?, comment? }
@@ -575,7 +577,9 @@ export const delivery = {
 
   /**
    * POST /api/delivery
-   * Body: { number, date, supplierId?, lines: DeliveryLineInput[] }
+   * Body: { externalNumber?, date, supplierId?, lines: DeliveryLineInput[] }
+   * number is NOT sent — the server allocates it automatically. The
+   * caller-supplied reference goes in externalNumber (nullable).
    * Line requires sku, amount, net, tax. rebate→0, transactedAmount→amount.
    * → 201 { delivery: Delivery }
    */
@@ -585,7 +589,9 @@ export const delivery = {
 
   /**
    * PATCH /api/delivery/:id
-   * Body: partial { number?, date?, supplierId?, lines? }.
+   * Body: partial { externalNumber?, date?, supplierId?, lines? }.
+   * number is read-only and cannot be edited. externalNumber is editable and
+   * can be cleared by sending null or an empty string.
    * If lines present, replaces all lines; if omitted, lines unchanged.
    * → 200 { delivery: Delivery }
    */
diff --git a/src/components/manifest/ManifestForm.jsx b/src/components/manifest/ManifestForm.jsx
index ca4afe7..8d6de61 100644
--- a/src/components/manifest/ManifestForm.jsx
+++ b/src/components/manifest/ManifestForm.jsx
@@ -35,6 +35,7 @@ class ManifestForm extends PureComponent {
       date: '',
       partyId: null,
       number: '',
+      externalNumber: '',
       lines: [emptyLine()],
       saving: false,
     };
@@ -43,6 +44,8 @@ class ManifestForm extends PureComponent {
     this.handlePartyChange = this.handlePartyChange.bind(this);
     this.handleDateChange = this.handleDateChange.bind(this);
     this.handleNumberChange = this.handleNumberChange.bind(this);
+    this.handleExternalNumberChange =
+      this.handleExternalNumberChange.bind(this);
     this.handleLineChange = this.handleLineChange.bind(this);
     this.handleAddLine = this.handleAddLine.bind(this);
     this.handleRemoveLine = this.handleRemoveLine.bind(this);
@@ -122,6 +125,8 @@ class ManifestForm extends PureComponent {
         date: dateInputValue(doc.date),
         partyId: doc[cfg.partyField],
         number: doc.number ?? '',
+        externalNumber:
+          doc.externalNumber != null ? String(doc.externalNumber) : '',
         lines,
       });
     } catch (err) {
@@ -157,6 +162,10 @@ class ManifestForm extends PureComponent {
     this.setState({ number });
   }
 
+  handleExternalNumberChange(externalNumber) {
+    this.setState({ externalNumber });
+  }
+
   handleLineChange(key, field, value) {
     this.setState((prev) => ({
       lines: prev.lines.map((line) =>
@@ -188,11 +197,16 @@ class ManifestForm extends PureComponent {
       body = buildManifestBody(
         {
           number: this.state.number,
+          externalNumber: this.state.externalNumber,
           date: this.state.date,
           partyId: this.state.partyId,
           lines: this.state.lines,
         },
-        { partyField: cfg.partyField, requireAtLeastOne },
+        {
+          partyField: cfg.partyField,
+          requireAtLeastOne,
+          externalNumber: cfg.externalNumber,
+        },
       );
     } catch (err) {
       notifyError(err);
@@ -225,6 +239,8 @@ class ManifestForm extends PureComponent {
         date: dateInputValue(doc.date),
         partyId: doc[cfg.partyField],
         number: doc.number ?? '',
+        externalNumber:
+          doc.externalNumber != null ? String(doc.externalNumber) : '',
         lines:
           apiLines.length > 0 ? apiLines.map(lineFromApi) : [emptyLine()],
         saving: false,
@@ -280,6 +296,7 @@ class ManifestForm extends PureComponent {
       date,
       partyId,
       number,
+      externalNumber,
       saving,
     } = this.state;
 
@@ -307,10 +324,12 @@ class ManifestForm extends PureComponent {
           partyId={partyId}
           date={date}
           number={number}
+          externalNumber={externalNumber}
           saving={saving}
           onPartyChange={this.handlePartyChange}
           onDateChange={this.handleDateChange}
           onNumberChange={this.handleNumberChange}
+          onExternalNumberChange={this.handleExternalNumberChange}
         />
         {status === 'ready' ? this.renderArticles() : null}
       </PanelTileGrid>
diff --git a/src/components/manifest/ManifestHeader.jsx b/src/components/manifest/ManifestHeader.jsx
index 39e069b..1e23d21 100644
--- a/src/components/manifest/ManifestHeader.jsx
+++ b/src/components/manifest/ManifestHeader.jsx
@@ -4,7 +4,7 @@ import Stack from '@mui/material/Stack';
 import TextField from '@mui/material/TextField';
 import SingleLineTextEdit from '../SingleLineTextEdit';
 import { PanelTile } from '../panels';
-import { partyDisplayName } from './manifestConfig';
+import { manifestConfig, partyDisplayName } from './manifestConfig';
 
 class ManifestHeader extends PureComponent {
   constructor(props) {
@@ -27,12 +27,20 @@ class ManifestHeader extends PureComponent {
       partyId,
       date,
       number,
+      externalNumber,
       saving,
       onDateChange,
       onNumberChange,
+      onExternalNumberChange,
     } = this.props;
 
-    const selected = parties.find((row) => row.id === partyId) ?? null;
+    // Delivery: number is server-allocated/read-only; the caller reference
+    // lives in the editable externalNumber field.
+    const cfg = manifestConfig(kind);
+    const useExternalNumber = Boolean(cfg.externalNumber);
+
+    const selected =
+      parties.find((row) => row.id === partyId) ?? null;
 
     return (
       <PanelTile wide={3} minHeight={160} color={headerColor} title="Kopfdaten">
@@ -80,10 +88,20 @@ class ManifestHeader extends PureComponent {
             size="small"
             label="Nummer"
             value={number}
-            disabled={saving}
+            disabled={saving || useExternalNumber}
             onChange={onNumberChange}
             sx={{ minWidth: 180, flex: 1 }}
           />
+          {useExternalNumber ? (
+            <SingleLineTextEdit
+              size="small"
+              label="Referenz"
+              value={externalNumber ?? ''}
+              disabled={saving}
+              onChange={onExternalNumberChange}
+              sx={{ minWidth: 180, flex: 1 }}
+            />
+          ) : null}
         </Stack>
       </PanelTile>
     );
diff --git a/src/components/manifest/ManifestList.jsx b/src/components/manifest/ManifestList.jsx
index 056968f..bd8ad41 100644
--- a/src/components/manifest/ManifestList.jsx
+++ b/src/components/manifest/ManifestList.jsx
@@ -24,6 +24,7 @@ import {
   formatDate,
   loadParties,
   manifestConfig,
+  numberDisplay,
   partyDisplayName,
   sortDocs,
 } from './manifestConfig';
@@ -169,6 +170,9 @@ class ManifestList extends PureComponent {
                   <TableHead>
                     <TableRow>
                       <TableCell>Nummer</TableCell>
+                      {cfg.externalNumber ? (
+                        <TableCell>Referenz</TableCell>
+                      ) : null}
                       <TableCell>{cfg.dateLabel}</TableCell>
                       <TableCell>{cfg.partyLabel}</TableCell>
                       <TableCell padding="checkbox" />
@@ -183,6 +187,11 @@ class ManifestList extends PureComponent {
                         onClick={() => this.handleEdit(row)}
                       >
                         <TableCell>{row.number}</TableCell>
+                        {cfg.externalNumber ? (
+                          <TableCell>
+                            {numberDisplay(row.externalNumber)}
+                          </TableCell>
+                        ) : null}
                         <TableCell>{formatDate(row.date)}</TableCell>
                         <TableCell>{this.partyName(row[partyField])}</TableCell>
                         <TableCell
diff --git a/src/components/manifest/manifestConfig.js b/src/components/manifest/manifestConfig.js
index 115e4fd..9c1e7fa 100644
--- a/src/components/manifest/manifestConfig.js
+++ b/src/components/manifest/manifestConfig.js
@@ -44,6 +44,16 @@ export function formatDate(iso) {
   return d.toLocaleDateString('de-DE');
 }
 
+/**
+ * Delivery documents have a server-allocated, read-only `number` plus an
+ * optional user-entered `externalNumber`. Returns the display value for a
+ * field, defaulting to a dash when empty.
+ */
+export function numberDisplay(value) {
+  if (value == null || String(value).trim() === '') return '–';
+  return String(value);
+}
+
 export function dateInputValue(iso) {
   if (!iso) return '';
   const d = new Date(iso);
@@ -105,20 +115,35 @@ export function buildLines(lines, { requireAtLeastOne }) {
 }
 
 /**
- * @param {{ number: string, date: string, partyId: number|null, lines: object[] }} form
- * @param {{ partyField: 'supplierId'|'entityId', requireAtLeastOne: boolean }} opts
+ * @param {{ number: string, externalNumber?: string, date: string, partyId: number|null, lines: object[] }} form
+ * @param {{ partyField: 'supplierId'|'entityId', requireAtLeastOne: boolean, externalNumber?: boolean }} opts
  */
-export function buildManifestBody(form, { partyField, requireAtLeastOne }) {
-  const number = String(form.number ?? '').trim();
+export function buildManifestBody(
+  form,
+  { partyField, requireAtLeastOne, externalNumber: useExternalNumber },
+) {
   const date = form.date;
-  if (!number) throw new Error('Nummer fehlt.');
   if (!date) throw new Error('Datum fehlt.');
 
-  const body = {
-    number,
-    date,
-    lines: buildLines(form.lines, { requireAtLeastOne }),
-  };
+  let body;
+  if (useExternalNumber) {
+    // Delivery: number is server-allocated/read-only. The caller-supplied
+    // reference goes in externalNumber (nullable; empty string → null).
+    const externalNumber = String(form.externalNumber ?? '').trim();
+    body = {
+      externalNumber: externalNumber || null,
+      date,
+      lines: buildLines(form.lines, { requireAtLeastOne }),
+    };
+  } else {
+    const number = String(form.number ?? '').trim();
+    if (!number) throw new Error('Nummer fehlt.');
+    body = {
+      number,
+      date,
+      lines: buildLines(form.lines, { requireAtLeastOne }),
+    };
+  }
   if (form.partyId != null) body[partyField] = form.partyId;
   else if (!requireAtLeastOne) body[partyField] = null;
   return body;
@@ -192,6 +217,9 @@ export function manifestConfig(kind) {
       listPromise: (ctx) => ctx.deliveries ?? ctx.deliveryPromise,
       partiesByIdFromList: (parties) =>
         Object.fromEntries(parties.map((row) => [row.id, row])),
+      // Delivery uses a server-allocated read-only number plus an optional
+      // caller-supplied external reference.
+      externalNumber: true,
     };
   }
   if (kind === 'quote') {
diff --git a/src/theme/themes/default.js b/src/theme/themes/default.js
index 2874e89..20052f6 100644
--- a/src/theme/themes/default.js
+++ b/src/theme/themes/default.js
@@ -25,5 +25,17 @@ export function createDefaultTheme() {
       },
     },
     nav,
+    components: {
+      MuiMenu: {
+        defaultProps: {
+          transitionDuration: 0,
+        },
+      },
+      MuiPopover: {
+        defaultProps: {
+          transitionDuration: 0,
+        },
+      },
+    },
   });
 }