diff --git a/tools/releasetools/merge_target_files.py b/tools/releasetools/merge_target_files.py
new file mode 100755
index 0000000..b02363c
--- /dev/null
+++ b/tools/releasetools/merge_target_files.py
@@ -0,0 +1,679 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2019 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License. You may obtain a copy of
+# the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License 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.
+
+"""
+This script merges two partial target files packages (one of which contains
+system files, and the other contains non-system files) together, producing a
+complete target files package that can be used to generate an OTA package.
+
+Usage: merge_target_files.py [args]
+
+  --system-target-files system-target-files-zip-archive
+      The input target files package containing system bits. This is a zip
+      archive.
+
+  --other-target-files other-target-files-zip-archive
+      The input target files package containing other bits. This is a zip
+      archive.
+
+  --output-target-files output-target-files-package
+      The output merged target files package. Also a zip archive.
+"""
+
+from __future__ import print_function
+
+import argparse
+import fnmatch
+import logging
+import os
+import sys
+import zipfile
+
+import common
+import add_img_to_target_files
+
+logger = logging.getLogger(__name__)
+OPTIONS = common.OPTIONS
+OPTIONS.verbose = True
+
+# system_extract_as_is_item_list is a list of items to extract from the partial
+# system target files package as is, meaning these items will land in the
+# output target files package exactly as they appear in the input partial
+# system target files package.
+
+system_extract_as_is_item_list = [
+    'META/apkcerts.txt',
+    'META/filesystem_config.txt',
+    'META/root_filesystem_config.txt',
+    'META/system_manifest.xml',
+    'META/system_matrix.xml',
+    'META/update_engine_config.txt',
+    'PRODUCT/*',
+    'ROOT/*',
+    'SYSTEM/*',
+]
+
+# system_extract_special_item_list is a list of items to extract from the
+# partial system target files package that need some special processing, such
+# as some sort of combination with items from the partial other target files
+# package.
+
+system_extract_special_item_list = [
+    'META/*',
+]
+
+# system_misc_info_keys is a list of keys to obtain from the system instance of
+# META/misc_info.txt. The remaining keys from the other instance.
+
+system_misc_info_keys = [
+    'avb_system_hashtree_enable',
+    'avb_system_add_hashtree_footer_args',
+    'avb_system_key_path',
+    'avb_system_algorithm',
+    'avb_system_rollback_index_location',
+    'avb_product_hashtree_enable',
+    'avb_product_add_hashtree_footer_args',
+    'avb_product_services_hashtree_enable',
+    'avb_product_services_add_hashtree_footer_args',
+    'system_root_image',
+    'root_dir',
+    'ab_update',
+    'default_system_dev_certificate',
+    'system_size',
+]
+
+# other_extract_as_is_item_list is a list of items to extract from the partial
+# other target files package as is, meaning these items will land in the output
+# target files package exactly as they appear in the input partial other target
+# files package.
+
+other_extract_as_is_item_list = [
+    'META/boot_filesystem_config.txt',
+    'META/otakeys.txt',
+    'META/releasetools.py',
+    'META/vendor_filesystem_config.txt',
+    'META/vendor_manifest.xml',
+    'META/vendor_matrix.xml',
+    'BOOT/*',
+    'DATA/*',
+    'ODM/*',
+    'OTA/android-info.txt',
+    'PREBUILT_IMAGES/*',
+    'RADIO/*',
+    'VENDOR/*',
+]
+
+# other_extract_for_merge_item_list is a list of items to extract from the
+# partial other target files package that need some special processing, such as
+# some sort of combination with items from the partial system target files
+# package.
+
+other_extract_special_item_list = [
+    'META/*',
+]
+
+
+def extract_items(target_files, target_files_temp_dir, extract_item_list):
+  """Extract items from target files to temporary directory.
+
+  This function extracts from the specified target files zip archive into the
+  specified temporary directory, the items specified in the extract item list.
+
+  Args:
+    target_files: The target files zip archive from which to extract items.
+
+    target_files_temp_dir: The temporary directory where the extracted items
+    will land.
+
+    extract_item_list: A list of items to extract.
+
+  Returns:
+    On success, 0. Otherwise, a non-zero exit code from unzip.
+  """
+
+  logger.info('extracting from %s', target_files)
+
+  # Filter the extract_item_list to remove any items that do not exist in the
+  # zip file. Otherwise, the extraction step will fail.
+
+  with zipfile.ZipFile(
+      target_files,
+      'r',
+      allowZip64=True) as target_files_zipfile:
+    target_files_namelist = target_files_zipfile.namelist()
+
+  filtered_extract_item_list = []
+  for pattern in extract_item_list:
+    matching_namelist = fnmatch.filter(target_files_namelist, pattern)
+    if not matching_namelist:
+      logger.warning('no match for %s', pattern)
+    else:
+      filtered_extract_item_list.append(pattern)
+
+  # Extract the filtered_extract_item_list from target_files into
+  # target_files_temp_dir.
+
+  # TODO(b/124464492): Extend common.UnzipTemp() to handle this use case.
+  command = [
+      'unzip',
+      '-n',
+      '-q',
+      '-d', target_files_temp_dir,
+      target_files
+  ] + filtered_extract_item_list
+
+  result = common.RunAndWait(command, verbose=True)
+
+  if result != 0:
+    logger.error('extract_items command %s failed %d', str(command), result)
+    return result
+
+  return 0
+
+
+def process_ab_partitions_txt(
+    system_target_files_temp_dir,
+    other_target_files_temp_dir,
+    output_target_files_temp_dir):
+  """Perform special processing for META/ab_partitions.txt
+
+  This function merges the contents of the META/ab_partitions.txt files from
+  the system directory and the other directory, placing the merged result in
+  the output directory. The precondition in that the files are already
+  extracted. The post condition is that the output META/ab_partitions.txt
+  contains the merged content. The format for each ab_partitions.txt a one
+  partition name per line. The output file contains the union of the parition
+  names.
+
+  Args:
+    system_target_files_temp_dir: The name of a directory containing the
+    special items extracted from the system target files package.
+
+    other_target_files_temp_dir: The name of a directory containing the
+    special items extracted from the other target files package.
+
+    output_target_files_temp_dir: The name of a directory that will be used
+    to create the output target files package after all the special cases
+    are processed.
+  """
+
+  system_ab_partitions_txt = os.path.join(
+      system_target_files_temp_dir, 'META', 'ab_partitions.txt')
+
+  other_ab_partitions_txt = os.path.join(
+      other_target_files_temp_dir, 'META', 'ab_partitions.txt')
+
+  with open(system_ab_partitions_txt) as f:
+    system_ab_partitions = f.read().splitlines()
+
+  with open(other_ab_partitions_txt) as f:
+    other_ab_partitions = f.read().splitlines()
+
+  output_ab_partitions = set(system_ab_partitions + other_ab_partitions)
+
+  output_ab_partitions_txt = os.path.join(
+      output_target_files_temp_dir, 'META', 'ab_partitions.txt')
+
+  with open(output_ab_partitions_txt, 'w') as output:
+    for partition in sorted(output_ab_partitions):
+      output.write('%s\n' % partition)
+
+
+def process_misc_info_txt(
+    system_target_files_temp_dir,
+    other_target_files_temp_dir,
+    output_target_files_temp_dir):
+  """Perform special processing for META/misc_info.txt
+
+  This function merges the contents of the META/misc_info.txt files from the
+  system directory and the other directory, placing the merged result in the
+  output directory. The precondition in that the files are already extracted.
+  The post condition is that the output META/misc_info.txt contains the merged
+  content.
+
+  Args:
+    system_target_files_temp_dir: The name of a directory containing the
+    special items extracted from the system target files package.
+
+    other_target_files_temp_dir: The name of a directory containing the
+    special items extracted from the other target files package.
+
+    output_target_files_temp_dir: The name of a directory that will be used
+    to create the output target files package after all the special cases
+    are processed.
+  """
+
+  def read_helper(d):
+    misc_info_txt = os.path.join(d, 'META', 'misc_info.txt')
+    with open(misc_info_txt) as f:
+      return list(f.read().splitlines())
+
+  system_info_dict = common.LoadDictionaryFromLines(
+      read_helper(system_target_files_temp_dir))
+
+  # We take most of the misc info from the other target files.
+
+  merged_info_dict = common.LoadDictionaryFromLines(
+      read_helper(other_target_files_temp_dir))
+
+  # Replace certain values in merged_info_dict with values from
+  # system_info_dict. TODO(b/124467065): This should be more flexible than
+  # using the hard-coded system_misc_info_keys.
+
+  for key in system_misc_info_keys:
+    merged_info_dict[key] = system_info_dict[key]
+
+  output_misc_info_txt = os.path.join(
+      output_target_files_temp_dir,
+      'META', 'misc_info.txt')
+
+  sorted_keys = sorted(merged_info_dict.keys())
+
+  with open(output_misc_info_txt, 'w') as output:
+    for key in sorted_keys:
+      output.write('{}={}\n'.format(key, merged_info_dict[key]))
+
+
+def process_file_contexts_bin(temp_dir, output_target_files_temp_dir):
+  """Perform special processing for META/file_contexts.bin.
+
+  This function combines plat_file_contexts and vendor_file_contexts, which are
+  expected to already be extracted in temp_dir, to produce a merged
+  file_contexts.bin that will land in temp_dir at META/file_contexts.bin.
+
+  Args:
+    temp_dir: The name of a scratch directory that this function can use for
+    intermediate files generated during processing.
+
+    output_target_files_temp_dir: The name of the working directory that must
+    already contain plat_file_contexts and vendor_file_contexts (in the
+    appropriate sub directories), and to which META/file_contexts.bin will be
+    written.
+
+  Returns:
+    On success, 0. Otherwise, a non-zero exit code.
+  """
+
+  # To create a merged file_contexts.bin file, we use the system and vendor
+  # file contexts files as input, the m4 tool to combine them, the sorting tool
+  # to sort, and finally the sefcontext_compile tool to generate the final
+  # output. We currently omit a checkfc step since the files had been checked
+  # as part of the build.
+
+  # The m4 step concatenates the two input files contexts files. Since m4
+  # writes to stdout, we receive that into an array of bytes, and then write it
+  # to a file.
+
+  # Collect the file contexts that we're going to combine from SYSTEM, VENDOR,
+  # PRODUCT, and ODM. We require SYSTEM and VENDOR, but others are optional.
+
+  file_contexts_list = []
+
+  for partition in ['SYSTEM', 'VENDOR', 'PRODUCT', 'ODM']:
+    prefix = 'plat' if partition == 'SYSTEM' else partition.lower()
+
+    file_contexts = os.path.join(
+        output_target_files_temp_dir,
+        partition, 'etc', 'selinux', prefix + '_file_contexts')
+
+    mandatory = partition in ['SYSTEM', 'VENDOR']
+
+    if mandatory or os.path.isfile(file_contexts):
+      file_contexts_list.append(file_contexts)
+    else:
+      logger.warning('file not found: %s', file_contexts)
+
+  command = ['m4', '--fatal-warnings', '-s'] + file_contexts_list
+
+  merged_content = common.RunAndCheckOutput(command, verbose=False)
+
+  merged_file_contexts_txt = os.path.join(temp_dir, 'merged_file_contexts.txt')
+
+  with open(merged_file_contexts_txt, 'wb') as f:
+    f.write(merged_content)
+
+  # The sort step sorts the concatenated file.
+
+  sorted_file_contexts_txt = os.path.join(temp_dir, 'sorted_file_contexts.txt')
+  command = ['fc_sort', merged_file_contexts_txt, sorted_file_contexts_txt]
+
+  # TODO(b/124521133): Refector RunAndWait to raise exception on failure.
+  result = common.RunAndWait(command, verbose=True)
+
+  if result != 0:
+    return result
+
+  # Finally, the compile step creates the final META/file_contexts.bin.
+
+  file_contexts_bin = os.path.join(
+      output_target_files_temp_dir,
+      'META', 'file_contexts.bin')
+
+  command = [
+      'sefcontext_compile',
+      '-o', file_contexts_bin,
+      sorted_file_contexts_txt,
+  ]
+
+  result = common.RunAndWait(command, verbose=True)
+
+  if result != 0:
+    return result
+
+  return 0
+
+
+def process_special_cases(
+    temp_dir,
+    system_target_files_temp_dir,
+    other_target_files_temp_dir,
+    output_target_files_temp_dir):
+  """Perform special-case processing for certain target files items.
+
+  Certain files in the output target files package require special-case
+  processing. This function performs all that special-case processing.
+
+  Args:
+    temp_dir: The name of a scratch directory that this function can use for
+    intermediate files generated during processing.
+
+    system_target_files_temp_dir: The name of a directory containing the
+    special items extracted from the system target files package.
+
+    other_target_files_temp_dir: The name of a directory containing the
+    special items extracted from the other target files package.
+
+    output_target_files_temp_dir: The name of a directory that will be used
+    to create the output target files package after all the special cases
+    are processed.
+
+  Returns:
+    On success, 0. Otherwise, a non-zero exit code.
+  """
+
+  process_ab_partitions_txt(
+      system_target_files_temp_dir=system_target_files_temp_dir,
+      other_target_files_temp_dir=other_target_files_temp_dir,
+      output_target_files_temp_dir=output_target_files_temp_dir)
+
+  process_misc_info_txt(
+      system_target_files_temp_dir=system_target_files_temp_dir,
+      other_target_files_temp_dir=other_target_files_temp_dir,
+      output_target_files_temp_dir=output_target_files_temp_dir)
+
+  result = process_file_contexts_bin(
+      temp_dir=temp_dir,
+      output_target_files_temp_dir=output_target_files_temp_dir)
+
+  if result != 0:
+    return result
+
+  return 0
+
+
+def merge_target_files(
+    temp_dir,
+    system_target_files,
+    other_target_files,
+    output_target_files):
+  """Merge two target files packages together.
+
+  This function takes system and other target files packages as input, performs
+  various file extractions, special case processing, and finally creates a
+  merged zip archive as output.
+
+  Args:
+    temp_dir: The name of a directory we use when we extract items from the
+    input target files packages, and also a scratch directory that we use for
+    temporary files.
+
+    system_target_files: The name of the zip archive containing the system
+    partial target files package.
+
+    other_target_files: The name of the zip archive containing the other
+    partial target files package.
+
+    output_target_files: The name of the output zip archive target files
+    package created by merging system and other.
+
+  Returns:
+    On success, 0. Otherwise, a non-zero exit code.
+  """
+
+  # Create directory names that we'll use when we extract files from system,
+  # and other, and for zipping the final output.
+
+  system_target_files_temp_dir = os.path.join(temp_dir, 'system')
+  other_target_files_temp_dir = os.path.join(temp_dir, 'other')
+  output_target_files_temp_dir = os.path.join(temp_dir, 'output')
+
+  # Extract "as is" items from the input system partial target files package.
+  # We extract them directly into the output temporary directory since the
+  # items do not need special case processing.
+
+  result = extract_items(
+      target_files=system_target_files,
+      target_files_temp_dir=output_target_files_temp_dir,
+      extract_item_list=system_extract_as_is_item_list)
+
+  if result != 0:
+    return result
+
+  # Extract "as is" items from the input other partial target files package. We
+  # extract them directly into the output temporary directory since the items
+  # do not need special case processing.
+
+  result = extract_items(
+      target_files=other_target_files,
+      target_files_temp_dir=output_target_files_temp_dir,
+      extract_item_list=other_extract_as_is_item_list)
+
+  if result != 0:
+    return result
+
+  # Extract "special" items from the input system partial target files package.
+  # We extract these items to different directory since they require special
+  # processing before they will end up in the output directory.
+
+  result = extract_items(
+      target_files=system_target_files,
+      target_files_temp_dir=system_target_files_temp_dir,
+      extract_item_list=system_extract_special_item_list)
+
+  if result != 0:
+    return result
+
+  # Extract "special" items from the input other partial target files package.
+  # We extract these items to different directory since they require special
+  # processing before they will end up in the output directory.
+
+  result = extract_items(
+      target_files=other_target_files,
+      target_files_temp_dir=other_target_files_temp_dir,
+      extract_item_list=other_extract_special_item_list)
+
+  if result != 0:
+    return result
+
+  # Now that the temporary directories contain all the extracted files, perform
+  # special case processing on any items that need it. After this function
+  # completes successfully, all the files we need to create the output target
+  # files package are in place.
+
+  result = process_special_cases(
+      temp_dir=temp_dir,
+      system_target_files_temp_dir=system_target_files_temp_dir,
+      other_target_files_temp_dir=other_target_files_temp_dir,
+      output_target_files_temp_dir=output_target_files_temp_dir)
+
+  if result != 0:
+    return result
+
+  # Regenerate IMAGES in the temporary directory.
+
+  add_img_args = [
+      '--verbose',
+      output_target_files_temp_dir,
+  ]
+
+  add_img_to_target_files.main(add_img_args)
+
+  # Finally, create the output target files zip archive.
+
+  output_zip = os.path.abspath(output_target_files)
+  output_target_files_list = os.path.join(temp_dir, 'output.list')
+  output_target_files_meta_dir = os.path.join(
+      output_target_files_temp_dir, 'META')
+
+  command = [
+      'find',
+      output_target_files_meta_dir,
+  ]
+  # TODO(bpeckham): sort this to be more like build.
+  meta_content = common.RunAndCheckOutput(command, verbose=False)
+  command = [
+      'find',
+      output_target_files_temp_dir,
+      '-path',
+      output_target_files_meta_dir,
+      '-prune',
+      '-o',
+      '-print'
+  ]
+  # TODO(bpeckham): sort this to be more like build.
+  other_content = common.RunAndCheckOutput(command, verbose=False)
+
+  with open(output_target_files_list, 'wb') as f:
+    f.write(meta_content)
+    f.write(other_content)
+
+  command = [
+      # TODO(124468071): Use soong_zip from otatools.zip
+      'prebuilts/build-tools/linux-x86/bin/soong_zip',
+      '-d',
+      '-o', output_zip,
+      '-C', output_target_files_temp_dir,
+      '-l', output_target_files_list,
+  ]
+  logger.info('creating %s', output_target_files)
+  result = common.RunAndWait(command, verbose=True)
+
+  if result != 0:
+    logger.error('zip command %s failed %d', str(command), result)
+    return result
+
+  return 0
+
+
+def merge_target_files_with_temp_dir(
+    system_target_files,
+    other_target_files,
+    output_target_files,
+    keep_tmp):
+  """Manage the creation and cleanup of the temporary directory.
+
+  This function wraps merge_target_files after first creating a temporary
+  directory. It also cleans up the temporary directory.
+
+  Args:
+    system_target_files: The name of the zip archive containing the system
+    partial target files package.
+
+    other_target_files: The name of the zip archive containing the other
+    partial target files package.
+
+    output_target_files: The name of the output zip archive target files
+    package created by merging system and other.
+
+    keep_tmp: Keep the temporary directory after processing is complete.
+
+  Returns:
+    On success, 0. Otherwise, a non-zero exit code.
+  """
+
+  # Create a temporary directory. This will serve as the parent of directories
+  # we use when we extract items from the input target files packages, and also
+  # a scratch directory that we use for temporary files.
+
+  logger.info(
+      'starting: merge system %s and other %s into output %s',
+      system_target_files,
+      other_target_files,
+      output_target_files)
+
+  temp_dir = common.MakeTempDir(prefix='merge_target_files_')
+
+  try:
+    return merge_target_files(
+        temp_dir=temp_dir,
+        system_target_files=system_target_files,
+        other_target_files=other_target_files,
+        output_target_files=output_target_files)
+  except:
+    raise
+  finally:
+    if keep_tmp:
+      logger.info('keeping %s', temp_dir)
+    else:
+      common.Cleanup()
+
+
+def main():
+  """The main function.
+
+  Process command line arguments, then call merge_target_files_with_temp_dir to
+  perform the heavy lifting.
+
+  Returns:
+    On success, 0. Otherwise, a non-zero exit code.
+  """
+
+  common.InitLogging()
+
+  parser = argparse.ArgumentParser()
+
+  parser.add_argument(
+      '--system-target-files',
+      required=True,
+      help='The input target files package containing system bits.')
+
+  parser.add_argument(
+      '--other-target-files',
+      required=True,
+      help='The input target files package containing other bits.')
+
+  parser.add_argument(
+      '--output-target-files',
+      required=True,
+      help='The output merged target files package.')
+
+  parser.add_argument(
+      '--keep-tmp',
+      required=False,
+      action='store_true',
+      help='Keep the temporary directories after execution.')
+
+  args = parser.parse_args()
+
+  return merge_target_files_with_temp_dir(
+      system_target_files=args.system_target_files,
+      other_target_files=args.other_target_files,
+      output_target_files=args.output_target_files,
+      keep_tmp=args.keep_tmp)
+
+
+if __name__ == '__main__':
+  sys.exit(main())