diff --git a/pydantic_xml/model.py b/pydantic_xml/model.py
index 1ee18ef..aa6c895 100644
--- a/pydantic_xml/model.py
+++ b/pydantic_xml/model.py
@@ -304,12 +304,13 @@ def to_xml_tree(
         assert self.__xml_serializer__ is not None, f"model {type(self).__name__} is partially initialized"
 
         root = XmlElement(tag=self.__xml_serializer__.element_name, nsmap=self.__xml_serializer__.nsmap)
+        encoded = pdc.to_jsonable_python(
+            self,
+            by_alias=False,
+            fallback=lambda obj: obj if not isinstance(obj, ElementT) else None,  # for raw fields support
+        )
         self.__xml_serializer__.serialize(
-            root, self, pdc.to_jsonable_python(
-                self,
-                by_alias=False,
-                fallback=lambda obj: obj if not isinstance(obj, ElementT) else None,  # for raw fields support
-            ),
+            root, self, encoded,
             skip_empty=skip_empty,
             exclude_none=exclude_none,
             exclude_unset=exclude_unset,
diff --git a/pydantic_xml/serializers/factories/model.py b/pydantic_xml/serializers/factories/model.py
index 39fcf4a..5de15cf 100644
--- a/pydantic_xml/serializers/factories/model.py
+++ b/pydantic_xml/serializers/factories/model.py
@@ -9,8 +9,11 @@
 import pydantic_xml as pxml
 from pydantic_xml import errors, utils
 from pydantic_xml.element import XmlElementReader, XmlElementWriter, is_element_nill, make_element_nill
+from pydantic_xml.element.native import ElementT
 from pydantic_xml.fields import ComputedXmlEntityInfo, XmlEntityInfoP, extract_field_xml_entity_info
+from pydantic_xml.serializers.factories.primitive import AttributeSerializer
 from pydantic_xml.serializers.serializer import SearchMode, Serializer
+from pydantic_xml.serializers.factories.raw import ElementSerializer as RawElementSerializer
 from pydantic_xml.typedefs import EntityLocation, Location, NsMap
 from pydantic_xml.utils import QName, merge_nsmaps, select_ns
 
@@ -51,6 +54,29 @@ def _check_extra(cls, error_title: str, element: XmlElementReader) -> None:
         if line_errors:
             raise pd.ValidationError.from_exception_data(title=error_title, line_errors=line_errors)
 
+    def _keep_extra(self, element: XmlElementReader) -> Dict:
+        """Get a struct of extra (=unmapped) data from the XML.
+
+        Attributes are put in key-value pairs directly.
+        Child elements are put in as native Elements.
+        """
+        result = {}
+
+        # Extract un-mapped attributes:
+        if attrs := element._state.attrib:
+            for name, value in attrs.items():
+                if name not in self._field_serializers:
+                    result[name] = value
+
+        # `get_unbound` returns paths of leaf-level elements of type `XmlElement`, while
+        # we want to produce the same result of a raw-element, which is `ElemenT`
+        # So manually find un-mapped elements and get the native element back:
+        for sub_element in element._state.elements:
+            if (tag := sub_element.tag) not in self._field_serializers:
+                result[tag] = sub_element.to_native()
+
+        return result
+
 
 class ModelSerializer(BaseModelSerializer):
     @classmethod
@@ -163,7 +189,23 @@ def serialize(
         if self._model.__xml_skip_empty__ is not None:
             skip_empty = self._model.__xml_skip_empty__
 
-        for field_name, field_serializer in self._field_serializers.items():
+        all_fields = list(self._field_serializers.keys())
+        all_fields += [k for k in encoded.keys() if k not in all_fields]
+        # ^ avoid sets to preserve order of fields
+
+        for field_name in all_fields:
+            field_serializer = self._field_serializers.get(field_name, None)
+            if field_serializer is None:  # Probably from an `extra` field
+                if encoded[field_name] is None:
+                    field_serializer = RawElementSerializer(field_name, ns=None,
+                                                            nsmap=None,
+                                                            search_mode=SearchMode.ORDERED,
+                                                            computed=False)
+                else:
+                    field_serializer = AttributeSerializer(field_name, ns=None,
+                                                           nsmap=None, computed=False)
+
+
             if field_name in self._fields_serialization_exclude:
                 continue
             if exclude_unset and field_name not in value.__pydantic_fields_set__:
@@ -212,8 +254,13 @@ def deserialize(
         if field_errors:
             raise utils.into_validation_error(title=self._model.__name__, errors_map=field_errors)
 
-        if self._model.model_config.get('extra', 'ignore') == 'forbid':
+        config_extra = self._model.model_config.get('extra', 'ignore')
+        if config_extra == 'forbid':
             self._check_extra(self._model.__name__, element)
+        elif config_extra == 'allow':
+            result.update(
+                self._keep_extra(element)
+            )
 
         try:
             return self._model.model_validate(result, strict=False, context=context)
diff --git a/tests/test_extra_allow.py b/tests/test_extra_allow.py
new file mode 100644
index 0000000..98cdf06
--- /dev/null
+++ b/tests/test_extra_allow.py
@@ -0,0 +1,148 @@
+from pydantic import ValidationError
+from pydantic_xml import BaseXmlModel, attr, element
+from pydantic_xml.element.native import ElementT
+
+import pytest
+
+from tests.helpers import assert_xml_equal
+
+
+def test_extra_attributes_ignored():
+    class TestModel(BaseXmlModel, tag='model', extra='ignore'):
+        prop1: str = attr()
+        data: str
+
+    xml = '''
+    <model prop1="p1" prop2="p2">text</model>
+    '''
+
+    actual_obj = TestModel.from_xml(xml)
+    assert actual_obj.model_extra is None
+
+
+def test_extra_attributes_forbidden():
+    class TestModel(BaseXmlModel, tag='model', extra='forbid'):
+        prop1: str = attr()
+        data: str
+
+    xml = '''
+    <model prop1="p1" prop2="p2">text</model>
+    '''
+
+    with pytest.raises(ValidationError):
+        _ = TestModel.from_xml(xml)
+
+
+def test_extra_attributes():
+    class TestModel(BaseXmlModel, tag='model', extra='allow'):
+        prop1: str = attr()
+        data: str
+
+    xml = '''
+    <model prop1="p1" prop2="p2">text</model>
+    '''
+
+    actual_obj = TestModel.from_xml(xml)
+    assert 'p2' == actual_obj.model_extra['prop2']
+
+
+def test_extra_elements():
+
+    class TestModelChild(BaseXmlModel, tag='child'):
+        data: str
+
+    class TestModel(BaseXmlModel, tag='model', extra='allow'):
+        child: TestModelChild
+
+    xml = '''
+    <model>
+        <child>hello world!</child>
+        <extra_child>hi again...</extra_child>
+        <extra_nested>
+            <extra_sub>1</extra_sub>
+            <extra_sub>2</extra_sub>
+            <extra_sub>3</extra_sub>
+            <extra_subsub>
+                <extra_subsubsub>3.14</extra_subsubsub>
+            </extra_subsub>
+        </extra_nested>
+    </model>
+    '''
+
+    actual_obj = TestModel.from_xml(xml)
+    assert 'hello world!' == actual_obj.child.data
+    assert 'extra_child' in actual_obj.model_extra
+    assert 'extra_nested' in actual_obj.model_extra
+
+
+def test_raw_save():
+    # Just for debugging!!!
+
+    class TestModel(BaseXmlModel, tag='model', arbitrary_types_allowed=True):
+        extra_nested: ElementT = element()
+
+    xml = '''
+    <model>
+        <extra_nested>
+            <extra_sub>1</extra_sub>
+            <extra_sub>2</extra_sub>
+            <extra_sub>3</extra_sub>
+            <extra_subsub subprop="x">
+                <extra_subsubsub>3.14</extra_subsubsub>
+            </extra_subsub>
+        </extra_nested>
+    </model>
+    '''
+
+    actual_obj = TestModel.from_xml(xml)
+    actual_xml = actual_obj.to_xml()
+    assert_xml_equal(actual_xml, xml)
+
+
+def test_extra_save():
+
+    class TestModelChild(BaseXmlModel, tag='child'):
+        data: str
+
+    class TestModel(BaseXmlModel, tag='model', extra='allow'):
+        prop1: str = attr()
+        child: TestModelChild
+
+    xml = '''
+    <model prop1="p1" prop2="p2" prop3="p3">
+        <child>hello world!</child>
+        <extra_child>hi again...</extra_child>
+        <extra_nested>
+            <extra_sub>1</extra_sub>
+            <extra_sub>2</extra_sub>
+            <extra_sub>3</extra_sub>
+            <extra_subsub subprop="x">
+                <extra_subsubsub>3.14</extra_subsubsub>
+            </extra_subsub>
+        </extra_nested>
+    </model>
+    '''
+
+    actual_obj = TestModel.from_xml(xml)
+    actual_xml = actual_obj.to_xml()
+    assert_xml_equal(actual_xml, xml)
+
+
+def test_extra_save_order():
+
+    class TestModelChild(BaseXmlModel, tag='child'):
+        data: str
+
+    class TestModel(BaseXmlModel, tag='model', extra='allow', search_mode='ordered'):
+        child: TestModelChild
+
+    xml = '''
+    <model>
+        <other_child>Hi there</other_child>
+        <child>Hello world!</child>
+    </model>
+    '''
+
+    actual_obj = TestModel.from_xml(xml)
+    actual_xml = actual_obj.to_xml()
+    assert_xml_equal(actual_xml, xml)