diff --git a/README.rst b/README.rst
index 419f68f..f851fb4 100644
--- a/README.rst
+++ b/README.rst
@@ -273,6 +273,25 @@ Validating a list of TaxIDs against a Tree data structure in ``pickle`` format:
   taxonomy-resolver validate -in tree.pickle -taxids testdata/taxids_validate.txt
 
 
+Load a previously built Tree data structure in ``pickle`` format and search for one or more TaxIDs (for example human, TaxID '9606'). Included, excluded and filter lists can be optionally passed as shown above.
+
+.. code-block:: bash
+
+  taxonomy-resolver search -in tree.pickle -taxid "9606" -out testdata/taxids_human.txt
+
+Writing the 'complete' human sub-tree (i.e. all levels of the hierarchy) in ``newick`` format can be done via the build command and passing a TaxID filter file, which can be generated by running the search command shown previously.
+ 
+.. code-block:: bash
+
+  taxonomy-resolver build -in tree.pickle -inf pickle -taxidsf testdata/taxids_human.txt -out testdata/taxids_human.nwk -outf newick
+
+Alternatively, ``newick`` output can be generated for the 'local' human sub-tree (i.e. species and sub-species levels only), directly using the search command, as shown below:
+
+.. code-block:: bash
+
+  taxonomy-resolver search -in tree.pickle -taxid "9606" -out testdata/taxids_human_local.nwk -outf newick
+
+
 Contributing
 ============
 
diff --git a/taxonomyresolver/cli.py b/taxonomyresolver/cli.py
index 3bc6577..c0717fb 100644
--- a/taxonomyresolver/cli.py
+++ b/taxonomyresolver/cli.py
@@ -17,6 +17,7 @@
     print_and_exit,
     validate_inputs_outputs,
 )
+from taxonomyresolver.tree import write_tree
 
 
 # reusing click args and options
@@ -174,7 +175,7 @@ def download(
     default="pickle",
     required=False,
     multiple=False,
-    help="Output format (currently: 'pickle').",
+    help="Output format (currently: 'pickle' or 'newick').",
 )
 @click.option(
     "-taxidsf",
@@ -289,6 +290,16 @@ def build(
     multiple=False,
     help="Input format (currently: 'pickle').",
 )
+@click.option(
+    "-outf",
+    "--outformat",
+    "outformat",
+    type=str,
+    default="txt",
+    required=False,
+    multiple=False,
+    help="Input format (currently: 'txt' or 'newick').",
+)
 @click.option(
     "-taxid",
     "--taxid",
@@ -354,6 +365,7 @@ def search(
     infile: str,
     outfile: str | None,
     informat: str,
+    outformat: str,
     taxids: str | None,
     taxidincludes: str | None,
     taxidsexcludes: str | None,
@@ -421,10 +433,20 @@ def search(
         ignoreinvalid=ignoreinvalid,
     )
     if outfile:
-        with open(outfile, "w") as outf:
-            if tax_ids:
-                outf.write("\n".join(list(tax_ids)))
-        logging.info(f"Wrote list of TaxIDS in {outfile}.")
+        if outformat == "newick" and resolver.tree is not None and tax_ids:
+            subset = (
+                resolver.tree[resolver.tree["id"].isin(list(tax_ids))]
+                .sort_values("lft")
+                .reset_index()
+            )
+            write_tree(subset, outputfile=outfile, outputformat=outformat)
+        else:
+            with open(outfile, "w") as outf:
+                if tax_ids:
+
+                    outf.write("\n".join(list(tax_ids)))
+                    outf.write("\n".join(list(tax_ids)))
+        logging.info(f"Wrote list of TaxIDS in {outfile} in '{outformat}' format.")
     else:
         try:
             if tax_ids:
diff --git a/taxonomyresolver/tree.py b/taxonomyresolver/tree.py
index f655f96..6a36735 100644
--- a/taxonomyresolver/tree.py
+++ b/taxonomyresolver/tree.py
@@ -24,6 +24,7 @@
     split_line,
     tree_reparenting,
     tree_traversal,
+    tree_to_newick,
 )
 
 
@@ -84,11 +85,14 @@ def write_tree(
 
     :param tree: pandas DataFrame
     :param outputfile: Path to outputfile
-    :param outputformat: currently "pickle" format
+    :param outputformat: currently "pickle" or "newick" format
     :return: (side-effects) writes to file
     """
     if outputformat == "pickle" and tree is not None:
         tree.to_pickle(outputfile, protocol=4)
+    elif outputformat == "newick" and tree is not None:
+        with open(outputfile, "w") as outfile:
+            outfile.write(tree_to_newick(tree) + "\n")
     # elif outputformat == "shelve":
     #     with shelve.open(outputfile) as outfile:
     #         outfile["tree"] = tree
diff --git a/taxonomyresolver/utils.py b/taxonomyresolver/utils.py
index bcc8841..37be153 100644
--- a/taxonomyresolver/utils.py
+++ b/taxonomyresolver/utils.py
@@ -15,6 +15,7 @@
 import pandas as pd
 import requests
 from tqdm import tqdm
+from collections import defaultdict
 
 
 def get_logging_level(level: str = "INFO"):
@@ -229,3 +230,39 @@ def get_parents(tree: pd.DataFrame, lft: int, rgt: int) -> list:
     :return: list of TaxIDs
     """
     return list(tree[(tree["lft"] < lft) & (tree["rgt"] > rgt)]["id"].values)
+
+
+def tree_to_newick(tree: pd.DataFrame) -> str:
+    """
+    Converts a hierarchical tree DataFrame into a Newick string.
+
+    :param tree: pandas DataFrame
+    :return: A string in Newick format.
+    """
+
+    # find the root of the tree (where id == parent_id)
+    try:
+        root_id = tree[tree["id"] == tree["parent_id"]]["id"].iloc[0]
+    except IndexError:
+        # assume the tree is sorted and use the first line (sort of rootless)
+        root_id = tree["id"].iloc[0]
+
+    # build a dictionary of children for each node
+    children = defaultdict(list)
+    for _, row in tqdm(tree.iterrows(), total=len(tree), desc="Generating Newick"):
+        if row["id"] != row["parent_id"]:
+            children[row["parent_id"]].append(row["id"])
+
+    # process nodes in reverse order of `depth` (from leaf nodes to the root)
+    newick = {}
+    for depth in sorted(tree["depth"].unique(), reverse=True):
+        nodes_at_depth = tree[tree["depth"] == depth]["id"]
+        for node_id in nodes_at_depth:
+            if node_id in children:
+                subtree = ",".join(newick[child] for child in children[node_id])
+                newick[node_id] = f"({subtree}){node_id}"
+            else:
+                # leaf node
+                newick[node_id] = f"{node_id}"
+
+    return newick[root_id] + ";"
diff --git a/testdata/taxids_human.nwk b/testdata/taxids_human.nwk
new file mode 100644
index 0000000..86b12e6
--- /dev/null
+++ b/testdata/taxids_human.nwk
@@ -0,0 +1 @@
+(63221,741158)9606;
diff --git a/testdata/taxids_human.txt b/testdata/taxids_human.txt
new file mode 100644
index 0000000..f1387a5
--- /dev/null
+++ b/testdata/taxids_human.txt
@@ -0,0 +1,3 @@
+9606
+741158
+63221
\ No newline at end of file
diff --git a/tests/test_tree.py b/tests/test_tree.py
index bd66b2c..22589c5 100644
--- a/tests/test_tree.py
+++ b/tests/test_tree.py
@@ -13,7 +13,7 @@
 import pytest
 
 from taxonomyresolver import TaxonResolver
-from taxonomyresolver.utils import load_logging
+from taxonomyresolver.utils import load_logging, tree_to_newick
 
 
 @pytest.fixture
@@ -339,3 +339,12 @@ def test_resolver_validate_mock_tree(self, context, cwd):
         assert resolver.validate(taxidinclude=["9"])
         assert resolver.validate(taxidinclude=["10"])
         assert not resolver.validate(taxidinclude=["9606"])
+
+    def test_resolver_mock_tree_to_newick(self, context, cwd):
+        resolver = TaxonResolver(logging=context)
+        resolver.load(os.path.join(cwd, "../testdata/tree_mock.pickle"), "pickle")
+        taxidfilter = ["28", "29"]
+        resolver.filter(taxidfilter)
+        if resolver.tree is not None:
+            newick = tree_to_newick(resolver.tree)
+            assert newick == "(((((((28,29)27)24)18)9)4)2)1;"