diff --git a/concatenator/harmony/__init__.py b/concatenator/harmony/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/concatenator/harmony/cli.py b/concatenator/harmony/cli.py
new file mode 100644
index 0000000..3329095
--- /dev/null
+++ b/concatenator/harmony/cli.py
@@ -0,0 +1,33 @@
+"""A Harmony CLI wrapper around the concatenate-batcher"""
+from argparse import ArgumentParser
+
+import harmony
+
+from concatenator.harmony.service_adapter import StitcheeAdapter as HarmonyAdapter
+
+
+def main(config: harmony.util.Config = None) -> None:
+    """Parse command line arguments and invoke the service to respond to them.
+
+    Parameters
+    ----------
+    config : harmony.util.Config
+        harmony.util.Config is injectable for tests
+
+    Returns
+    -------
+    None
+    """
+    parser = ArgumentParser(
+        prog="Stitchee", description="Run the STITCH by Extending a dimEnsion service"
+    )
+    harmony.setup_cli(parser)
+    args = parser.parse_args()
+    if harmony.is_harmony_cli(args):
+        harmony.run_cli(parser, args, HarmonyAdapter, cfg=config)
+    else:
+        parser.error("Only --harmony CLIs are supported")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/concatenator/harmony/download_worker.py b/concatenator/harmony/download_worker.py
new file mode 100644
index 0000000..0c177af
--- /dev/null
+++ b/concatenator/harmony/download_worker.py
@@ -0,0 +1,113 @@
+"""A utility for downloading multiple granules simultaneously"""
+
+import queue
+import re
+from copy import deepcopy
+from multiprocessing import Manager, Process
+from os import cpu_count
+from pathlib import Path
+from urllib.parse import urlparse
+
+from harmony.logging import build_logger
+from harmony.util import download
+
+
+def multi_core_download(urls, destination_dir, access_token, cfg, process_count=None):
+    """
+    A method which automagically scales downloads to the number of CPU
+    cores. For further explaination, see documentation on "multi-track
+    drifting"
+
+    Parameters
+    ----------
+    urls : list
+        list of urls to download
+    destination_dir : str
+        output path for downloaded files
+    access_token : str
+        access token as provided in Harmony input
+    cfg : dict
+        Harmony configuration information
+    process_count : int
+        Number of worker processes to run (expected >= 1)
+
+    Returns
+    -------
+    list
+        list of downloaded files as pathlib.Path objects
+    """
+
+    if process_count is None:
+        process_count = cpu_count()
+
+    with Manager() as manager:
+        url_queue = manager.Queue(len(urls))
+        path_list = manager.list()
+
+        for url in urls:
+            url_queue.put(url)
+
+        # Spawn worker processes
+        processes = []
+        for _ in range(process_count):
+            download_process = Process(
+                target=_download_worker,
+                args=(url_queue, path_list, destination_dir, access_token, cfg),
+            )
+            processes.append(download_process)
+            download_process.start()
+
+        # Ensure worker processes exit successfully
+        for process in processes:
+            process.join()
+            if process.exitcode != 0:
+                raise RuntimeError(f"Download failed - exit code: {process.exitcode}")
+
+            process.close()
+
+        path_list = deepcopy(path_list)  # ensure GC can cleanup multiprocessing
+
+    return [Path(path) for path in path_list]
+
+
+def _download_worker(url_queue, path_list, destination_dir, access_token, cfg):
+    """
+    A method to be executed in a separate process which processes the url_queue
+    and places paths to completed downloads into the path_list. Downloads are
+    handled by harmony.util.download
+
+    Parameters
+    ----------
+    url_queue : queue.Queue
+        URLs to process - should be filled from start and only decreases
+    path_list : list
+        paths to completed file downloads
+    destination_dir : str
+        output path for downloaded files
+    access_token : str
+        access token as provided in Harmony input
+    cfg : dict
+        Harmony configuration information
+    """
+
+    logger = build_logger(cfg)
+
+    while not url_queue.empty():
+        try:
+            url = url_queue.get_nowait()
+        except queue.Empty:
+            break
+
+        path = Path(
+            download(url, destination_dir, logger=logger, access_token=access_token, cfg=cfg)
+        )
+        filename_match = re.match(r".*\/(.+\..+)", urlparse(url).path)
+
+        if filename_match is not None:
+            filename = filename_match.group(1)
+            dest_path = path.parent.joinpath(filename)
+            path = path.rename(dest_path)
+        else:
+            logger.warning("Origin filename could not be assertained - %s", url)
+
+        path_list.append(str(path))
diff --git a/concatenator/harmony/service_adapter.py b/concatenator/harmony/service_adapter.py
new file mode 100644
index 0000000..5905229
--- /dev/null
+++ b/concatenator/harmony/service_adapter.py
@@ -0,0 +1,128 @@
+from pathlib import Path
+from tempfile import TemporaryDirectory
+from uuid import uuid4
+
+import pystac
+from harmony.adapter import BaseHarmonyAdapter
+from harmony.util import bbox_to_geometry
+from pystac import Item
+from pystac.item import Asset
+
+from concatenator.harmony.download_worker import multi_core_download
+from concatenator.harmony.util import (
+    _get_netcdf_urls,
+    _get_output_bounding_box,
+    _get_output_date_range,
+)
+from concatenator.stitchee import stitchee
+
+
+class StitcheeAdapter(BaseHarmonyAdapter):
+    """
+    A harmony-service-lib wrapper around the concatenate-batcher module.
+    This wrapper does not support Harmony calls that do not have STAC catalogs
+    as support for this behavior is being depreciated in harmony-service-lib
+    """
+
+    def __init__(self, message, catalog=None, config=None):
+        """
+        Constructs the adapter
+
+        Parameters
+        ----------
+        message : harmony.Message
+            The Harmony input which needs acting upon
+        catalog : pystac.Catalog
+            A STAC catalog containing the files on which to act
+        config : harmony.util.Config
+            The configuration values for this runtime environment.
+        """
+        super().__init__(message, catalog=catalog, config=config)
+
+    def invoke(self):
+        """
+        Primary entrypoint into the service wrapper. Overrides BaseHarmonyAdapter.invoke
+        """
+        if not self.catalog:
+            # Message-only support is being depreciated in Harmony, so we should expect to
+            # only see requests with catalogs when invoked with a newer Harmony instance
+            # https://github.com/nasa/harmony-service-lib-py/blob/21bcfbda17caf626fb14d2ac4f8673be9726b549/harmony/adapter.py#L71
+            raise RuntimeError("Invoking Batchee without a STAC catalog is not supported")
+
+        return self.message, self.process_catalog(self.catalog)
+
+    def process_catalog(self, catalog: pystac.Catalog):
+        """Converts a list of STAC catalogs into a list of lists of STAC catalogs."""
+        self.logger.info("process_catalog() started.")
+        try:
+            result = catalog.clone()
+            result.id = str(uuid4())
+            result.clear_children()
+
+            # Get all the items from the catalog, including from child or linked catalogs
+            items = list(self.get_all_catalog_items(catalog))
+
+            self.logger.info(f"length of items==={len(items)}.")
+
+            # Quick return if catalog contains no items
+            if len(items) == 0:
+                return result
+
+            # # --- Get granule filepaths (urls) ---
+            netcdf_urls: list[str] = _get_netcdf_urls(items)
+            self.logger.info(f"netcdf_urls==={netcdf_urls}.")
+
+            # -- Process metadata --
+            bounding_box: list | None = _get_output_bounding_box(items)
+            datetimes = _get_output_date_range(items)
+
+            # Items did not have a bbox; valid under spec
+            if bounding_box and len(bounding_box) == 0:
+                bounding_box = None
+
+            # -- Perform merging --
+            collection = self._get_item_source(items[0]).collection
+            filename = f"{collection}_merged.nc4"
+
+            with TemporaryDirectory() as temp_dir:
+                self.logger.info("Starting granule downloads")
+                input_files = multi_core_download(
+                    netcdf_urls, temp_dir, self.message.accessToken, self.config
+                )
+                self.logger.info("Finished granule downloads")
+
+                output_path = str(Path(temp_dir).joinpath(filename).resolve())
+
+                # # --- Run STITCHEE ---
+                stitchee(
+                    input_files,
+                    output_path,
+                    write_tmp_flat_concatenated=False,
+                    keep_tmp_files=False,
+                    concat_dim="mirror_step",  # This is currently set only for TEMPO
+                    logger=self.logger,
+                )
+                staged_url = self._stage(output_path, filename, "application/x-netcdf4")
+
+            # -- Output to STAC catalog --
+            result.clear_items()
+            properties = dict(
+                start_datetime=datetimes["start_datetime"], end_datetime=datetimes["end_datetime"]
+            )
+
+            item = Item(
+                str(uuid4()), bbox_to_geometry(bounding_box), bounding_box, None, properties
+            )
+            asset = Asset(
+                staged_url, title=filename, media_type="application/x-netcdf4", roles=["data"]
+            )
+            item.add_asset("data", asset)
+            result.add_item(item)
+
+            self.logger.info("STAC catalog creation complete.")
+
+            return result
+
+        except Exception as service_exception:
+            self.logger.error(service_exception, exc_info=1)
+            raise service_exception
diff --git a/concatenator/harmony/util.py b/concatenator/harmony/util.py
new file mode 100644
index 0000000..f77aeb9
--- /dev/null
+++ b/concatenator/harmony/util.py
@@ -0,0 +1,98 @@
+"""Misc utility functions"""
+from datetime import datetime
+
+from pystac import Asset, Item
+
+VALID_EXTENSIONS = (".nc4", ".nc")
+VALID_MEDIA_TYPES = ["application/x-netcdf", "application/x-netcdf4"]
+
+
+def _is_netcdf_asset(asset: Asset) -> bool:
+    """Check that a `pystac.Asset` is a valid NetCDF-4 granule. This can be
+    ascertained via either the media type or by checking the extension of
+    granule itself if that media type is absent.
+
+    """
+    return asset.media_type in VALID_MEDIA_TYPES or (
+        asset.media_type is None and asset.href.lower().endswith(VALID_EXTENSIONS)
+    )
+
+
+def _get_item_url(item: Item) -> str | None:
+    """Check the `pystac.Item` for the first asset with the `data` role and a
+    valid input format. If there are no matching assets, return None
+
+    """
+    return next(
+        (
+            asset.href
+            for asset in item.assets.values()
+            if "data" in (asset.roles or []) and _is_netcdf_asset(asset)
+        ),
+        None,
+    )
+
+
+def _get_netcdf_urls(items: list[Item]) -> list[str]:
+    """Iterate through a list of `pystac.Item` instances, from the input
+    `pystac.Catalog`. Extract the `pystac.Asset.href` for the first asset
+    of each item that has a role of "data". If there are any items that do
+    not have a data asset, then raise an exception.
+
+    """
+    catalog_urls = [_get_item_url(item) for item in items]
+
+    if None in catalog_urls:
+        raise RuntimeError("Some input granules do not have NetCDF-4 assets.")
+
+    return catalog_urls  # type: ignore[return-value]
+
+
+def _get_output_bounding_box(input_items: list[Item]) -> list[float]:
+    """Create a bounding box that is the maximum combined extent of all input
+    `pystac.Item` bounding box extents.
+
+    """
+    bounding_box = input_items[0].bbox
+
+    for item in input_items:
+        bounding_box[0] = min(bounding_box[0], item.bbox[0])
+        bounding_box[1] = min(bounding_box[1], item.bbox[1])
+        bounding_box[2] = max(bounding_box[2], item.bbox[2])
+        bounding_box[3] = max(bounding_box[3], item.bbox[3])
+
+    return bounding_box
+
+
+def _get_output_date_range(input_items: list[Item]) -> dict[str, str]:
+    """Create a dictionary of start and end datetime, which encompasses the
+    full temporal range of all input `pystac.Item` instances. This output
+    dictionary will be used for the `properties` of the output Zarr store
+    `pystac.Item`.
+
+    """
+    start_datetime, end_datetime = _get_item_date_range(input_items[0])
+
+    for item in input_items:
+        new_start_datetime, new_end_datetime = _get_item_date_range(item)
+        start_datetime = min(start_datetime, new_start_datetime)
+        end_datetime = max(end_datetime, new_end_datetime)
+
+    return {"start_datetime": start_datetime.isoformat(), "end_datetime": end_datetime.isoformat()}
+
+
+def _get_item_date_range(item: Item) -> tuple[datetime, datetime]:
+    """A helper function to retrieve the temporal range from a `pystac.Item`
+    instance. If the `pystac.Item.datetime` property exists, there is a
+    single datetime associated with the granule, otherwise there will be a
+    start and end time contained within the `pystac.Item` metadata.
+
+    """
+    if item.datetime is None:
+        start_datetime = item.common_metadata.start_datetime
+        end_datetime = item.common_metadata.end_datetime
+    else:
+        start_datetime = item.datetime
+        end_datetime = item.datetime
+
+    return start_datetime, end_datetime