diff --git a/src/dynamodb_encryption_sdk/internal/utils.py b/src/dynamodb_encryption_sdk/internal/utils.py
index bb133766..93bdbca3 100644
--- a/src/dynamodb_encryption_sdk/internal/utils.py
+++ b/src/dynamodb_encryption_sdk/internal/utils.py
@@ -16,17 +16,20 @@
     No guarantee is provided on the modules and APIs within this
     namespace staying consistent. Directly reference at your own risk.
 """
+import copy
+from functools import partial
+
 import attr
 import botocore.client
 
 from dynamodb_encryption_sdk.encrypted import CryptoConfig
 from dynamodb_encryption_sdk.encrypted.item import decrypt_python_item, encrypt_python_item
 from dynamodb_encryption_sdk.exceptions import InvalidArgumentError
-from dynamodb_encryption_sdk.structures import EncryptionContext, TableInfo
+from dynamodb_encryption_sdk.structures import CryptoAction, EncryptionContext, TableInfo
 from dynamodb_encryption_sdk.transform import dict_to_ddb
 
 try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
-    from typing import Any, Callable, Dict, Text  # noqa pylint: disable=unused-import
+    from typing import Any, Bool, Callable, Dict, Text  # noqa pylint: disable=unused-import
 except ImportError:  # pragma: no cover
     # We only actually need these imports when running the mypy checks
     pass
@@ -271,19 +274,22 @@ def encrypt_batch_write_item(encrypt_method, crypto_config_method, write_method,
     """Transparently encrypt multiple items before putting them in a batch request.
 
     :param callable encrypt_method: Method to use to encrypt items
-    :param callable crypto_config_method: Method that accepts ``kwargs`` and provides a :class:`CryptoConfig`
+    :param callable crypto_config_method: Method that accepts a table name string and provides a :class:`CryptoConfig`
     :param callable write_method: Method that writes to the table
     :param **kwargs: Keyword arguments to pass to ``write_method``
     :return: DynamoDB response
     :rtype: dict
     """
     request_crypto_config = kwargs.pop("crypto_config", None)
+    table_crypto_configs = {}
+    plaintext_items = copy.deepcopy(kwargs["RequestItems"])
 
     for table_name, items in kwargs["RequestItems"].items():
         if request_crypto_config is not None:
             crypto_config = request_crypto_config
         else:
             crypto_config = crypto_config_method(table_name=table_name)
+        table_crypto_configs[table_name] = crypto_config
 
         for pos, value in enumerate(items):
             for request_type, item in value.items():
@@ -293,4 +299,91 @@ def encrypt_batch_write_item(encrypt_method, crypto_config_method, write_method,
                         item=item["Item"],
                         crypto_config=crypto_config.with_item(_item_transformer(encrypt_method)(item["Item"])),
                     )
-    return write_method(**kwargs)
+
+    response = write_method(**kwargs)
+    return _process_batch_write_response(plaintext_items, response, table_crypto_configs)
+
+
+def _process_batch_write_response(request, response, table_crypto_config):
+    # type: (Dict, Dict, Dict[Text, CryptoConfig]) -> Dict
+    """Handle unprocessed items in the response from a transparently encrypted write.
+
+    :param dict request: The DynamoDB plaintext request dictionary
+    :param dict response: The DynamoDB response from the batch operation
+    :param Dict[Text, CryptoConfig] table_crypto_config: table level CryptoConfig used in encrypting the request items
+    :return: DynamoDB response, with any unprocessed items reverted back to the original plaintext values
+    :rtype: dict
+    """
+    try:
+        unprocessed_items = response["UnprocessedItems"]
+    except KeyError:
+        return response
+
+    # Unprocessed items need to be returned in their original state
+    for table_name, unprocessed in unprocessed_items.items():
+        original_items = request[table_name]
+        crypto_config = table_crypto_config[table_name]
+
+        if crypto_config.encryption_context.partition_key_name:
+            items_match = partial(_item_keys_match, crypto_config)
+        else:
+            items_match = partial(_item_attributes_match, crypto_config)
+
+        for pos, operation in enumerate(unprocessed):
+            for request_type, item in operation.items():
+                if request_type != "PutRequest":
+                    continue
+
+                for plaintext_item in original_items:
+                    if plaintext_item.get(request_type) and items_match(
+                        plaintext_item[request_type]["Item"], item["Item"]
+                    ):
+                        unprocessed[pos] = plaintext_item.copy()
+                        break
+
+    return response
+
+
+def _item_keys_match(crypto_config, item1, item2):
+    # type: (CryptoConfig, Dict, Dict) -> Bool
+    """Determines whether the values in the primary and sort keys (if they exist) are the same
+
+    :param CryptoConfig crypto_config: CryptoConfig used in encrypting the given items
+    :param dict item1: The first item to compare
+    :param dict item2: The second item to compare
+    :return: Bool response, True if the key attributes match
+    :rtype: bool
+    """
+    partition_key_name = crypto_config.encryption_context.partition_key_name
+    sort_key_name = crypto_config.encryption_context.sort_key_name
+
+    partition_keys_match = item1[partition_key_name] == item2[partition_key_name]
+
+    if sort_key_name is None:
+        return partition_keys_match
+
+    return partition_keys_match and item1[sort_key_name] == item2[sort_key_name]
+
+
+def _item_attributes_match(crypto_config, plaintext_item, encrypted_item):
+    # type: (CryptoConfig, Dict, Dict) -> Bool
+    """Determines whether the unencrypted values in the plaintext items attributes are the same as those in the
+    encrypted item. Essentially this uses brute force to cover when we don't know the primary and sort
+    index attribute names, since they can't be encrypted.
+
+    :param CryptoConfig crypto_config: CryptoConfig used in encrypting the given items
+    :param dict plaintext_item: The plaintext item
+    :param dict encrypted_item: The encrypted item
+    :return: Bool response, True if the unencrypted attributes in the plaintext item match those in
+    the encrypted item
+    :rtype: bool
+    """
+
+    for name, value in plaintext_item.items():
+        if crypto_config.attribute_actions.action(name) == CryptoAction.ENCRYPT_AND_SIGN:
+            continue
+
+        if encrypted_item.get(name) != value:
+            return False
+
+    return True
diff --git a/test/functional/encrypted/test_client.py b/test/functional/encrypted/test_client.py
index c928a55e..4498f954 100644
--- a/test/functional/encrypted/test_client.py
+++ b/test/functional/encrypted/test_client.py
@@ -17,6 +17,8 @@
 from ..functional_test_utils import example_table  # noqa pylint: disable=unused-import
 from ..functional_test_utils import (
     TEST_TABLE_NAME,
+    build_static_jce_cmp,
+    client_batch_items_unprocessed_check,
     client_cycle_batch_items_check,
     client_cycle_batch_items_check_paginators,
     client_cycle_single_item_check,
@@ -53,6 +55,12 @@ def _client_cycle_batch_items_check_paginators(materials_provider, initial_actio
     )
 
 
+def _client_batch_items_unprocessed_check(materials_provider, initial_actions, initial_item):
+    client_batch_items_unprocessed_check(
+        materials_provider, initial_actions, initial_item, TEST_TABLE_NAME, "us-west-2"
+    )
+
+
 def test_ephemeral_item_cycle(example_table, some_cmps, parametrized_actions, parametrized_item):
     """Test a small number of curated CMPs against a small number of curated items."""
     _client_cycle_single_item_check(some_cmps, parametrized_actions, parametrized_item)
@@ -68,6 +76,12 @@ def test_ephemeral_batch_item_cycle_paginators(example_table, some_cmps, paramet
     _client_cycle_batch_items_check_paginators(some_cmps, parametrized_actions, parametrized_item)
 
 
+def test_batch_item_unprocessed(example_table, parametrized_actions, parametrized_item):
+    """Test Unprocessed Items handling with a single ephemeral static CMP against a small number of curated items."""
+    cmp = build_static_jce_cmp("AES", 256, "HmacSHA256", 256)
+    _client_batch_items_unprocessed_check(cmp, parametrized_actions, parametrized_item)
+
+
 @pytest.mark.slow
 def test_ephemeral_item_cycle_slow(example_table, all_the_cmps, parametrized_actions, parametrized_item):
     """Test ALL THE CMPS against a small number of curated items."""
diff --git a/test/functional/encrypted/test_resource.py b/test/functional/encrypted/test_resource.py
index 3400906f..3c6a01e2 100644
--- a/test/functional/encrypted/test_resource.py
+++ b/test/functional/encrypted/test_resource.py
@@ -16,6 +16,8 @@
 from ..functional_test_utils import example_table  # noqa pylint: disable=unused-import
 from ..functional_test_utils import (
     TEST_TABLE_NAME,
+    build_static_jce_cmp,
+    resource_batch_items_unprocessed_check,
     resource_cycle_batch_items_check,
     set_parametrized_actions,
     set_parametrized_cmp,
@@ -35,11 +37,24 @@ def _resource_cycle_batch_items_check(materials_provider, initial_actions, initi
     resource_cycle_batch_items_check(materials_provider, initial_actions, initial_item, TEST_TABLE_NAME, "us-west-2")
 
 
+def _resource_batch_items_unprocessed_check(materials_provider, initial_actions, initial_item):
+    resource_batch_items_unprocessed_check(
+        materials_provider, initial_actions, initial_item, TEST_TABLE_NAME, "us-west-2"
+    )
+
+
 def test_ephemeral_batch_item_cycle(example_table, some_cmps, parametrized_actions, parametrized_item):
     """Test a small number of curated CMPs against a small number of curated items."""
     _resource_cycle_batch_items_check(some_cmps, parametrized_actions, parametrized_item)
 
 
+def test_batch_item_unprocessed(example_table, parametrized_actions, parametrized_item):
+    """Test Unprocessed Items handling with a single ephemeral static CMP against a small number of curated items."""
+    _resource_batch_items_unprocessed_check(
+        build_static_jce_cmp("AES", 256, "HmacSHA256", 256), parametrized_actions, parametrized_item
+    )
+
+
 @pytest.mark.travis_isolation
 @pytest.mark.slow
 def test_ephemeral_batch_item_cycle_slow(example_table, all_the_cmps, parametrized_actions, parametrized_item):
diff --git a/test/functional/encrypted/test_table.py b/test/functional/encrypted/test_table.py
index 4759edfe..fe9339ad 100644
--- a/test/functional/encrypted/test_table.py
+++ b/test/functional/encrypted/test_table.py
@@ -17,9 +17,11 @@
 from ..functional_test_utils import example_table  # noqa pylint: disable=unused-import
 from ..functional_test_utils import (
     TEST_TABLE_NAME,
+    build_static_jce_cmp,
     set_parametrized_actions,
     set_parametrized_cmp,
     set_parametrized_item,
+    table_batch_writer_unprocessed_items_check,
     table_cycle_batch_writer_check,
     table_cycle_check,
 )
@@ -48,6 +50,14 @@ def test_ephemeral_item_cycle_batch_writer(example_table, some_cmps, parametrize
     table_cycle_batch_writer_check(some_cmps, parametrized_actions, parametrized_item, TEST_TABLE_NAME, "us-west-2")
 
 
+def test_batch_writer_unprocessed(example_table, parametrized_actions, parametrized_item):
+    """Test Unprocessed Items handling with a single ephemeral static CMP against a small number of curated items."""
+    cmp = build_static_jce_cmp("AES", 256, "HmacSHA256", 256)
+    table_batch_writer_unprocessed_items_check(
+        cmp, parametrized_actions, parametrized_item, TEST_TABLE_NAME, "us-west-2"
+    )
+
+
 @pytest.mark.slow
 def test_ephemeral_item_cycle_slow(example_table, all_the_cmps, parametrized_actions, parametrized_item):
     """Test ALL THE CMPS against a small number of curated items."""
diff --git a/test/functional/functional_test_utils.py b/test/functional/functional_test_utils.py
index 9353408a..86ebf196 100644
--- a/test/functional/functional_test_utils.py
+++ b/test/functional/functional_test_utils.py
@@ -24,6 +24,7 @@
 import pytest
 from boto3.dynamodb.types import Binary
 from botocore.exceptions import NoRegionError
+from mock import patch
 from moto import mock_dynamodb2
 
 from dynamodb_encryption_sdk.delegated_keys.jce import JceNameLocalDelegatedKey
@@ -336,6 +337,10 @@ def diverse_item():
 _reserved_attributes = set([attr.value for attr in ReservedAttributes])
 
 
+def return_requestitems_as_unprocessed(*args, **kwargs):
+    return {"UnprocessedItems": kwargs["RequestItems"]}
+
+
 def check_encrypted_item(plaintext_item, ciphertext_item, attribute_actions):
     # Verify that all expected attributes are present
     ciphertext_attributes = set(ciphertext_item.keys())
@@ -374,12 +379,20 @@ def _nop_transformer(item):
     return item
 
 
+def assert_items_exist_in_list(source, expected, transformer):
+    for actual_item in source:
+        expected_item = _matching_key(actual_item, expected)
+        assert transformer(actual_item) == transformer(expected_item)
+
+
 def assert_equal_lists_of_items(actual, expected, transformer=_nop_transformer):
     assert len(actual) == len(expected)
+    assert_items_exist_in_list(actual, expected, transformer)
 
-    for actual_item in actual:
-        expected_item = _matching_key(actual_item, expected)
-        assert transformer(actual_item) == transformer(expected_item)
+
+def assert_list_of_items_contains(full, subset, transformer=_nop_transformer):
+    assert len(full) >= len(subset)
+    assert_items_exist_in_list(subset, full, transformer)
 
 
 def check_many_encrypted_items(actual, expected, attribute_actions, transformer=_nop_transformer):
@@ -479,6 +492,25 @@ def cycle_batch_writer_check(raw_table, encrypted_table, initial_actions, initia
     del items
 
 
+def batch_write_item_unprocessed_check(
+    encrypted, initial_item, write_transformer=_nop_transformer, table_name=TEST_TABLE_NAME
+):
+    """Check that unprocessed items in a batch result are unencrypted."""
+    items = _generate_items(initial_item, write_transformer)
+
+    request_items = {table_name: [{"PutRequest": {"Item": _item}} for _item in items]}
+    _put_result = encrypted.batch_write_item(RequestItems=request_items)
+
+    # we expect results to include Unprocessed items, or the test case is invalid!
+    unprocessed_items = _put_result["UnprocessedItems"]
+    assert unprocessed_items != {}
+
+    unprocessed = [operation["PutRequest"]["Item"] for operation in unprocessed_items[TEST_TABLE_NAME]]
+    assert_list_of_items_contains(items, unprocessed, transformer=_nop_transformer)
+
+    del items
+
+
 def cycle_item_check(plaintext_item, crypto_config):
     """Check that cycling (plaintext->encrypted->decrypted) an item has the expected results."""
     ciphertext_item = encrypt_python_item(plaintext_item, crypto_config)
@@ -527,6 +559,30 @@ def table_cycle_batch_writer_check(materials_provider, initial_actions, initial_
     cycle_batch_writer_check(table, e_table, initial_actions, initial_item)
 
 
+def table_batch_writer_unprocessed_items_check(
+    materials_provider, initial_actions, initial_item, table_name, region_name=None
+):
+    kwargs = {}
+    if region_name is not None:
+        kwargs["region_name"] = region_name
+    resource = boto3.resource("dynamodb", **kwargs)
+    table = resource.Table(table_name)
+
+    items = _generate_items(initial_item, _nop_transformer)
+    request_items = {table_name: [{"PutRequest": {"Item": _item}} for _item in items]}
+
+    with patch.object(table.meta.client, "batch_write_item") as batch_write_mock:
+        # Check that unprocessed items returned to a BatchWriter are successfully retried
+        batch_write_mock.side_effect = [{"UnprocessedItems": request_items}, {"UnprocessedItems": {}}]
+        e_table = EncryptedTable(table=table, materials_provider=materials_provider, attribute_actions=initial_actions)
+
+        with e_table.batch_writer() as writer:
+            for item in items:
+                writer.put_item(item)
+
+    del items
+
+
 def resource_cycle_batch_items_check(materials_provider, initial_actions, initial_item, table_name, region_name=None):
     kwargs = {}
     if region_name is not None:
@@ -550,6 +606,24 @@ def resource_cycle_batch_items_check(materials_provider, initial_actions, initia
     assert not e_scan_result["Items"]
 
 
+def resource_batch_items_unprocessed_check(
+    materials_provider, initial_actions, initial_item, table_name, region_name=None
+):
+    kwargs = {}
+    if region_name is not None:
+        kwargs["region_name"] = region_name
+    resource = boto3.resource("dynamodb", **kwargs)
+
+    with patch.object(resource, "batch_write_item", return_requestitems_as_unprocessed):
+        e_resource = EncryptedResource(
+            resource=resource, materials_provider=materials_provider, attribute_actions=initial_actions
+        )
+
+        batch_write_item_unprocessed_check(
+            encrypted=e_resource, initial_item=initial_item, write_transformer=dict_to_ddb, table_name=table_name
+        )
+
+
 def client_cycle_single_item_check(materials_provider, initial_actions, initial_item, table_name, region_name=None):
     check_attribute_actions = initial_actions.copy()
     check_attribute_actions.set_index_keys(*list(TEST_KEY.keys()))
@@ -600,6 +674,24 @@ def client_cycle_batch_items_check(materials_provider, initial_actions, initial_
     assert not e_scan_result["Items"]
 
 
+def client_batch_items_unprocessed_check(
+    materials_provider, initial_actions, initial_item, table_name, region_name=None
+):
+    kwargs = {}
+    if region_name is not None:
+        kwargs["region_name"] = region_name
+    client = boto3.client("dynamodb", **kwargs)
+
+    with patch.object(client, "batch_write_item", return_requestitems_as_unprocessed):
+        e_client = EncryptedClient(
+            client=client, materials_provider=materials_provider, attribute_actions=initial_actions
+        )
+
+        batch_write_item_unprocessed_check(
+            encrypted=e_client, initial_item=initial_item, write_transformer=dict_to_ddb, table_name=table_name
+        )
+
+
 def client_cycle_batch_items_check_paginators(
     materials_provider, initial_actions, initial_item, table_name, region_name=None
 ):
diff --git a/test/functional/internal/test_utils.py b/test/functional/internal/test_utils.py
new file mode 100644
index 00000000..1e52c0fd
--- /dev/null
+++ b/test/functional/internal/test_utils.py
@@ -0,0 +1,152 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+# http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+"""Test suite for ``dynamodb_encryption_sdk.internal.utils``."""
+import copy
+
+import pytest
+from mock import Mock
+
+from dynamodb_encryption_sdk.encrypted import CryptoConfig
+from dynamodb_encryption_sdk.identifiers import CryptoAction
+from dynamodb_encryption_sdk.internal.utils import encrypt_batch_write_item
+from dynamodb_encryption_sdk.material_providers import CryptographicMaterialsProvider
+from dynamodb_encryption_sdk.structures import AttributeActions, EncryptionContext
+from dynamodb_encryption_sdk.transform import dict_to_ddb
+
+from ..functional_test_utils import diverse_item
+
+
+def get_test_item(standard_dict_format, partition_key, sort_key=None):
+    attributes = diverse_item()
+
+    attributes["partition-key"] = partition_key
+    if sort_key is not None:
+        attributes["sort-key"] = sort_key
+
+    if not standard_dict_format:
+        attributes = dict_to_ddb(attributes)
+    return attributes
+
+
+def get_test_items(standard_dict_format, table_name="table", with_sort_keys=False):
+
+    if with_sort_keys:
+        items = [
+            get_test_item(standard_dict_format, partition_key="key-1", sort_key="sort-1"),
+            get_test_item(standard_dict_format, partition_key="key-2", sort_key="sort-1"),
+            get_test_item(standard_dict_format, partition_key="key-2", sort_key="sort-2"),
+        ]
+    else:
+        items = [
+            get_test_item(standard_dict_format, partition_key="key-1"),
+            get_test_item(standard_dict_format, partition_key="key-2"),
+        ]
+
+    for pos, item in enumerate(items):
+        item["encrypt-me"] = table_name + str(pos)
+
+    return {table_name: [{"PutRequest": {"Item": item}} for item in items]}
+
+
+def get_dummy_crypto_config(partition_key_name=None, sort_key_name=None, sign_keys=False):
+    context = EncryptionContext(partition_key_name=partition_key_name, sort_key_name=sort_key_name)
+    actions = AttributeActions(
+        default_action=CryptoAction.DO_NOTHING, attribute_actions={"encrypt-me": CryptoAction.ENCRYPT_AND_SIGN}
+    )
+    if sign_keys:
+        actions.attribute_actions["partition-key"] = CryptoAction.SIGN_ONLY
+        actions.attribute_actions["sort-key"] = CryptoAction.SIGN_ONLY
+
+    materials = Mock(spec=CryptographicMaterialsProvider)  # type: CryptographicMaterialsProvider
+    return CryptoConfig(materials_provider=materials, encryption_context=context, attribute_actions=actions)
+
+
+def check_encrypt_batch_write_item_call(request_items, crypto_config):
+    def dummy_encrypt(item, **kwargs):
+        result = item.copy()
+        result["encrypt-me"] = "pretend Im encrypted"
+        return result
+
+    # execute a batch write, but make the write method return ALL the provided items as unprocessed
+    result = encrypt_batch_write_item(
+        encrypt_method=dummy_encrypt,
+        write_method=lambda **kwargs: {"UnprocessedItems": kwargs["RequestItems"]},
+        crypto_config_method=lambda **kwargs: crypto_config,
+        RequestItems=copy.deepcopy(request_items),
+    )
+
+    # assert the returned items equal the submitted items
+    unprocessed = result["UnprocessedItems"]
+
+    assert unprocessed == request_items
+
+
+@pytest.mark.parametrize(
+    "items", (get_test_items(standard_dict_format=True), get_test_items(standard_dict_format=False))
+)
+def test_encrypt_batch_write_returns_plaintext_unprocessed_items_with_known_partition_key(items):
+    crypto_config = get_dummy_crypto_config("partition-key")
+    check_encrypt_batch_write_item_call(items, crypto_config)
+
+
+@pytest.mark.parametrize(
+    "items",
+    (
+        get_test_items(standard_dict_format=True, with_sort_keys=True),
+        get_test_items(standard_dict_format=False, with_sort_keys=True),
+    ),
+)
+def test_encrypt_batch_write_returns_plaintext_unprocessed_items_with_known_partition_and_sort_keys(items):
+    crypto_config = get_dummy_crypto_config("partition-key", "sort-key")
+    check_encrypt_batch_write_item_call(items, crypto_config)
+
+
+@pytest.mark.parametrize(
+    "items",
+    (
+        get_test_items(standard_dict_format=True),
+        get_test_items(standard_dict_format=False),
+        get_test_items(standard_dict_format=True, with_sort_keys=True),
+        get_test_items(standard_dict_format=False, with_sort_keys=True),
+    ),
+)
+def test_encrypt_batch_write_returns_plaintext_unprocessed_items_with_unknown_keys(items):
+    crypto_config = get_dummy_crypto_config(None, None)
+
+    check_encrypt_batch_write_item_call(items, crypto_config)
+
+
+@pytest.mark.parametrize(
+    "items",
+    (
+        get_test_items(standard_dict_format=True),
+        get_test_items(standard_dict_format=False),
+        get_test_items(standard_dict_format=True, with_sort_keys=True),
+        get_test_items(standard_dict_format=False, with_sort_keys=True),
+    ),
+)
+def test_encrypt_batch_write_returns_plaintext_unprocessed_items_with_unknown_signed_keys(items):
+    crypto_config = get_dummy_crypto_config(None, None, sign_keys=True)
+
+    check_encrypt_batch_write_item_call(items, crypto_config)
+
+
+def test_encrypt_batch_write_returns_plaintext_unprocessed_items_over_multiple_tables():
+    crypto_config = get_dummy_crypto_config("partition-key", "sort-key")
+
+    items = get_test_items(standard_dict_format=True, table_name="table-one", with_sort_keys=True)
+    more_items = get_test_items(standard_dict_format=False, table_name="table-two", with_sort_keys=True)
+    items.update(more_items)
+
+    check_encrypt_batch_write_item_call(items, crypto_config)