diff --git a/InvenTree/order/forms.py b/InvenTree/order/forms.py
index b5edec386a..bb6cb40889 100644
--- a/InvenTree/order/forms.py
+++ b/InvenTree/order/forms.py
@@ -14,6 +14,8 @@ from InvenTree.forms import HelperForm
 from InvenTree.fields import RoundingDecimalFormField
 from InvenTree.fields import DatePickerFormField
 
+import part.models
+
 from stock.models import StockLocation
 from .models import PurchaseOrder, PurchaseOrderLineItem, PurchaseOrderAttachment
 from .models import SalesOrder, SalesOrderLineItem, SalesOrderAttachment
@@ -211,7 +213,65 @@ class EditSalesOrderLineItemForm(HelperForm):
         ]
 
 
+class AllocateSerialsToSalesOrderForm(forms.Form):
+    """
+    Form for assigning stock to a sales order,
+    by serial number lookup
+    """
+
+    line = forms.ModelChoiceField(
+        queryset=SalesOrderLineItem.objects.all(),
+    )
+
+    part = forms.ModelChoiceField(
+        queryset=part.models.Part.objects.all(),
+    )
+
+    serials = forms.CharField(
+        label=_("Serial Numbers"),
+        required=True,
+        help_text=_('Enter stock item serial numbers'),
+    )
+
+    quantity = forms.IntegerField(
+        label=_('Quantity'),
+        required=True,
+        help_text=_('Enter quantity of stock items'),
+        initial=1,
+        min_value=1
+    )
+
+    class Meta:
+
+        fields = [
+            'line',
+            'part',
+            'serials',
+            'quantity',
+        ]
+
+
+class CreateSalesOrderAllocationForm(HelperForm):
+    """
+    Form for creating a SalesOrderAllocation item.
+    """
+
+    quantity = RoundingDecimalFormField(max_digits=10, decimal_places=5)
+
+    class Meta:
+        model = SalesOrderAllocation
+
+        fields = [
+            'line',
+            'item',
+            'quantity',
+        ]
+
+
 class EditSalesOrderAllocationForm(HelperForm):
+    """
+    Form for editing a SalesOrderAllocation item
+    """
 
     quantity = RoundingDecimalFormField(max_digits=10, decimal_places=5)
 
diff --git a/InvenTree/order/migrations/0043_auto_20210330_0013.py b/InvenTree/order/migrations/0043_auto_20210330_0013.py
new file mode 100644
index 0000000000..35c4b99bcb
--- /dev/null
+++ b/InvenTree/order/migrations/0043_auto_20210330_0013.py
@@ -0,0 +1,17 @@
+# Generated by Django 3.0.7 on 2021-03-29 13:13
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('order', '0042_auto_20210310_1619'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='salesorderlineitem',
+            unique_together=set(),
+        ),
+    ]
diff --git a/InvenTree/order/models.py b/InvenTree/order/models.py
index c3b33eaace..cb78eabc6a 100644
--- a/InvenTree/order/models.py
+++ b/InvenTree/order/models.py
@@ -663,7 +663,6 @@ class SalesOrderLineItem(OrderLineItem):
 
     class Meta:
         unique_together = [
-            ('order', 'part'),
         ]
 
     def fulfilled_quantity(self):
@@ -732,6 +731,12 @@ class SalesOrderAllocation(models.Model):
 
         errors = {}
 
+        try:
+            if not self.item:
+                raise ValidationError({'item': _('Stock item has not been assigned')})
+        except stock_models.StockItem.DoesNotExist:
+            raise ValidationError({'item': _('Stock item has not been assigned')})
+
         try:
             if not self.line.part == self.item.part:
                 errors['item'] = _('Cannot allocate stock item to a line with a different part')
diff --git a/InvenTree/order/templates/order/sales_order_detail.html b/InvenTree/order/templates/order/sales_order_detail.html
index 27bbd542dd..7b4a4ed4f7 100644
--- a/InvenTree/order/templates/order/sales_order_detail.html
+++ b/InvenTree/order/templates/order/sales_order_detail.html
@@ -275,15 +275,20 @@ $("#so-lines-table").inventreeTable({
                 if (row.part) {
                     var part = row.part_detail;
 
+                    if (part.trackable) {
+                        html += makeIconButton('fa-hashtag icon-green', 'button-add-by-sn', pk, '{% trans "Allocate serial numbers" %}');
+                    }
+
+                    html += makeIconButton('fa-sign-in-alt icon-green', 'button-add', pk, '{% trans "Allocate stock" %}');   
+
                     if (part.purchaseable) {
-                        html += makeIconButton('fa-shopping-cart', 'button-buy', row.part, '{% trans "Buy parts" %}');
+                        html += makeIconButton('fa-shopping-cart', 'button-buy', row.part, '{% trans "Purchase stock" %}');
                     }
                     
                     if (part.assembly) {
-                        html += makeIconButton('fa-tools', 'button-build', row.part, '{% trans "Build parts" %}');
+                        html += makeIconButton('fa-tools', 'button-build', row.part, '{% trans "Build stock" %}');
                     }
                     
-                    html += makeIconButton('fa-plus icon-green', 'button-add', pk, '{% trans "Allocate parts" %}');   
                 }
                 
                 html += makeIconButton('fa-edit icon-blue', 'button-edit', pk, '{% trans "Edit line item" %}');
@@ -316,10 +321,28 @@ function setupCallbacks() {
         var pk = $(this).attr('pk');
 
         launchModalForm(`/order/sales-order/line/${pk}/delete/`, {
-            reload: true,
+            success: reloadTable,
         });
     });
 
+    table.find(".button-add-by-sn").click(function() {
+        var pk = $(this).attr('pk');
+
+        inventreeGet(`/api/order/so-line/${pk}/`, {},
+            {
+                success: function(response) {
+                    launchModalForm('{% url "so-assign-serials" %}', {
+                        success: reloadTable,
+                        data: {
+                            line: pk,
+                            part: response.part, 
+                        }
+                    });
+                }
+            }
+        );
+    });
+
     table.find(".button-add").click(function() {
         var pk = $(this).attr('pk');
 
diff --git a/InvenTree/order/templates/order/so_allocate_by_serial.html b/InvenTree/order/templates/order/so_allocate_by_serial.html
new file mode 100644
index 0000000000..3e11d658c7
--- /dev/null
+++ b/InvenTree/order/templates/order/so_allocate_by_serial.html
@@ -0,0 +1,12 @@
+{% extends "modal_form.html" %}
+{% load i18n %}
+
+{% block pre_form_content %}
+
+<div class='alert alert-block alert-info'>
+    {% include "hover_image.html" with image=part.image hover=true %}{{ part }}
+    <hr>
+    {% trans "Allocate stock items by serial number" %}
+</div>
+
+{% endblock %}
\ No newline at end of file
diff --git a/InvenTree/order/test_sales_order.py b/InvenTree/order/test_sales_order.py
index c619aec5bc..0b37b96409 100644
--- a/InvenTree/order/test_sales_order.py
+++ b/InvenTree/order/test_sales_order.py
@@ -3,7 +3,6 @@
 from django.test import TestCase
 
 from django.core.exceptions import ValidationError
-from django.db.utils import IntegrityError
 
 from datetime import datetime, timedelta
 
@@ -73,10 +72,10 @@ class SalesOrderTest(TestCase):
         self.assertFalse(self.order.is_fully_allocated())
 
     def test_add_duplicate_line_item(self):
-        # Adding a duplicate line item to a SalesOrder must throw an error
+        # Adding a duplicate line item to a SalesOrder is accepted
         
-        with self.assertRaises(IntegrityError):
-            SalesOrderLineItem.objects.create(order=self.order, part=self.part)
+        for ii in range(1, 5):
+            SalesOrderLineItem.objects.create(order=self.order, part=self.part, quantity=ii)
 
     def allocate_stock(self, full=True):
 
diff --git a/InvenTree/order/urls.py b/InvenTree/order/urls.py
index 7707b73f37..97903d81c1 100644
--- a/InvenTree/order/urls.py
+++ b/InvenTree/order/urls.py
@@ -81,6 +81,7 @@ sales_order_urls = [
     # URLs for sales order allocations
     url(r'^allocation/', include([
         url(r'^new/', views.SalesOrderAllocationCreate.as_view(), name='so-allocation-create'),
+        url(r'^assign-serials/', views.SalesOrderAssignSerials.as_view(), name='so-assign-serials'),
         url(r'(?P<pk>\d+)/', include([
             url(r'^edit/', views.SalesOrderAllocationEdit.as_view(), name='so-allocation-edit'),
             url(r'^delete/', views.SalesOrderAllocationDelete.as_view(), name='so-allocation-delete'),
diff --git a/InvenTree/order/views.py b/InvenTree/order/views.py
index 2cd8e8a4cb..bdf0407603 100644
--- a/InvenTree/order/views.py
+++ b/InvenTree/order/views.py
@@ -7,9 +7,11 @@ from __future__ import unicode_literals
 
 from django.db import transaction
 from django.shortcuts import get_object_or_404
+from django.core.exceptions import ValidationError
 from django.urls import reverse
 from django.utils.translation import ugettext as _
 from django.views.generic import DetailView, ListView, UpdateView
+from django.views.generic.edit import FormMixin
 from django.forms import HiddenInput
 
 import logging
@@ -30,6 +32,7 @@ from . import forms as order_forms
 
 from InvenTree.views import AjaxView, AjaxCreateView, AjaxUpdateView, AjaxDeleteView
 from InvenTree.helpers import DownloadFile, str2bool
+from InvenTree.helpers import extract_serial_numbers
 from InvenTree.views import InvenTreeRoleMixin
 
 from InvenTree.status_codes import PurchaseOrderStatus, SalesOrderStatus, StockStatus
@@ -1291,11 +1294,179 @@ class SOLineItemDelete(AjaxDeleteView):
         }
 
 
+class SalesOrderAssignSerials(AjaxView, FormMixin):
+    """
+    View for assigning stock items to a sales order,
+    by serial number lookup.
+    """
+
+    model = SalesOrderAllocation
+    role_required = 'sales_order.change'
+    ajax_template_name = 'order/so_allocate_by_serial.html'
+    ajax_form_title = _('Allocate Serial Numbers')
+    form_class = order_forms.AllocateSerialsToSalesOrderForm
+
+    # Keep track of SalesOrderLineItem and Part references
+    line = None
+    part = None
+
+    def get_initial(self):
+        """
+        Initial values are passed as query params
+        """
+
+        initials = super().get_initial()
+
+        try:
+            self.line = SalesOrderLineItem.objects.get(pk=self.request.GET.get('line', None))
+            initials['line'] = self.line
+        except (ValueError, SalesOrderLineItem.DoesNotExist):
+            pass
+
+        try:
+            self.part = Part.objects.get(pk=self.request.GET.get('part', None))
+            initials['part'] = self.part
+        except (ValueError, Part.DoesNotExist):
+            pass
+
+        return initials
+
+    def post(self, request, *args, **kwargs):
+
+        self.form = self.get_form()
+
+        # Validate the form
+        self.form.is_valid()
+        self.validate()
+
+        valid = self.form.is_valid()
+
+        if valid:
+            self.allocate_items()
+
+        data = {
+            'form_valid': valid,
+            'form_errors': self.form.errors.as_json(),
+            'non_field_errors': self.form.non_field_errors().as_json(),
+            'success': _("Allocated") + f" {len(self.stock_items)} " + _("items")
+        }
+
+        return self.renderJsonResponse(request, self.form, data)
+
+    def validate(self):
+
+        data = self.form.cleaned_data
+
+        # Extract hidden fields from posted data
+        self.line = data.get('line', None)
+        self.part = data.get('part', None)
+
+        if self.line:
+            self.form.fields['line'].widget = HiddenInput()
+        else:
+            self.form.add_error('line', _('Select line item'))
+        
+        if self.part:
+            self.form.fields['part'].widget = HiddenInput()
+        else:
+            self.form.add_error('part', _('Select part'))
+
+        if not self.form.is_valid():
+            return
+
+        # Form is otherwise valid - check serial numbers
+        serials = data.get('serials', '')
+        quantity = data.get('quantity', 1)
+
+        # Save a list of serial_numbers
+        self.serial_numbers = None
+        self.stock_items = []
+
+        try:
+            self.serial_numbers = extract_serial_numbers(serials, quantity)
+
+            for serial in self.serial_numbers:
+                try:
+                    # Find matching stock item
+                    stock_item = StockItem.objects.get(
+                        part=self.part,
+                        serial=serial
+                    )
+                except StockItem.DoesNotExist:
+                    self.form.add_error(
+                        'serials',
+                        _('No matching item for serial') + f" '{serial}'"
+                    )
+                    continue
+
+                # Now we have a valid stock item - but can it be added to the sales order?
+                
+                # If not in stock, cannot be added to the order
+                if not stock_item.in_stock:
+                    self.form.add_error(
+                        'serials',
+                        f"'{serial}' " + _("is not in stock")
+                    )
+                    continue
+
+                # Already allocated to an order
+                if stock_item.is_allocated():
+                    self.form.add_error(
+                        'serials',
+                        f"'{serial}' " + _("already allocated to an order")
+                    )
+                    continue
+
+                # Add it to the list!
+                self.stock_items.append(stock_item)
+
+        except ValidationError as e:
+            self.form.add_error('serials', e.messages)
+
+    def allocate_items(self):
+        """
+        Create stock item allocations for each selected serial number
+        """
+
+        for stock_item in self.stock_items:
+            SalesOrderAllocation.objects.create(
+                item=stock_item,
+                line=self.line,
+                quantity=1,
+            )
+
+    def get_form(self):
+
+        form = super().get_form()
+
+        if self.line:
+            form.fields['line'].widget = HiddenInput()
+
+        if self.part:
+            form.fields['part'].widget = HiddenInput()
+
+        return form
+
+    def get_context_data(self):
+        return {
+            'line': self.line,
+            'part': self.part,
+        }
+
+    def get(self, request, *args, **kwargs):
+
+        return self.renderJsonResponse(
+            request,
+            self.get_form(),
+            context=self.get_context_data(),
+        )
+
+
 class SalesOrderAllocationCreate(AjaxCreateView):
     """ View for creating a new SalesOrderAllocation """
 
     model = SalesOrderAllocation
-    form_class = order_forms.EditSalesOrderAllocationForm
+    form_class = order_forms.CreateSalesOrderAllocationForm
     ajax_form_title = _('Allocate Stock to Order')
     
     def get_initial(self):