diff --git a/cat_merge/file_utils.py b/cat_merge/file_utils.py
index 6f9ee5f..1617011 100644
--- a/cat_merge/file_utils.py
+++ b/cat_merge/file_utils.py
@@ -6,6 +6,7 @@
 
 from cat_merge.model.merged_kg import MergedKG
 
+
 def get_files(filepath: str):
     node_files = []
     edge_files = []
@@ -17,15 +18,26 @@ def get_files(filepath: str):
             edge_files.append(f"{filepath}/{file}")
     return node_files, edge_files
 
+
 def read_dfs(files: List[str], add_provided_by: bool = True) -> List[pd.DataFrame]:
     dataframes = []
     for file in files:
+        dataframes.append(read_df(file, add_provided_by=add_provided_by))
+    return dataframes
+
+
+def read_df(file: str, add_provided_by: bool = True, index_column_is_id: bool = True):
+
+    if index_column_is_id:
         df = pd.read_csv(file, sep="\t", dtype="string", lineterminator="\n", index_col='id', quoting=csv.QUOTE_NONE)
         df.index.name = 'id'
-        if add_provided_by:
-            df["provided_by"] = os.path.basename(file)
-        dataframes.append(df)
-    return dataframes
+    else:
+        df = pd.read_csv(file, sep="\t", dtype="string", lineterminator="\n", quoting=csv.QUOTE_NONE)
+
+    if add_provided_by:
+        df["provided_by"] = os.path.basename(file)
+    return df
+
 
 def write_df(df: pd.DataFrame, filename: str):
     df.to_csv(filename, sep="\t")
diff --git a/cat_merge/mapping_utils.py b/cat_merge/mapping_utils.py
new file mode 100644
index 0000000..2157735
--- /dev/null
+++ b/cat_merge/mapping_utils.py
@@ -0,0 +1,17 @@
+import numpy as np
+from pandas.core.frame import DataFrame
+
+
+def apply_mappings(edges: DataFrame, mapping: DataFrame):
+
+    mapping_dict = mapping.set_index('subject_id')['object_id']
+
+    edges['original_subject'] = edges['subject']
+    edges['subject'].replace(mapping_dict, inplace=True)
+    edges['original_subject'] = np.where(edges.subject == edges.original_subject, None, edges.original_subject)
+
+    edges['original_object'] = edges['object']
+    edges['object'].replace(mapping_dict, inplace=True)
+    edges['original_object'] = np.where(edges.object == edges.original_object, None, edges.original_object)
+
+    return edges
diff --git a/cat_merge/merge.py b/cat_merge/merge.py
index af45eff..b94df44 100644
--- a/cat_merge/merge.py
+++ b/cat_merge/merge.py
@@ -7,6 +7,7 @@ def merge(
     input_dir: str = None,#typer.Option(None, help="Optional directory containing node and edge files"),
     edges: List[str] = None,#typer.Option(None, help="Optional list of edge files"),
     nodes: List[str] = None,#typer.Option(None, help="Optional list of node files"),
+    mapping: str = None,#typer.Option(None, help="Optional SSSOM mapping file")
     output_dir: str = "merged-output",#typer.Option("merged-output", help="Directory to output knowledge graph")
     merge_delimiter: str = "|",#typer.Option("|", help="Delimiter to use when merging categories and properties on duplicates")
     ):
@@ -21,8 +22,12 @@ def merge(
         node_dfs = read_dfs(node_files)
         edge_dfs = read_dfs(edge_files)
 
+    mapping_df = None
+    if mapping is not None:
+        mapping_df = read_df()
+
     write(
         name=name,
-        kg=merge_kg(node_dfs=node_dfs, edge_dfs=edge_dfs, merge_delimiter=merge_delimiter),
+        kg=merge_kg(node_dfs=node_dfs, edge_dfs=edge_dfs, mapping=mapping_df, merge_delimiter=merge_delimiter),
         output_dir=output_dir
     )
diff --git a/cat_merge/merge_utils.py b/cat_merge/merge_utils.py
index 0b96a1e..e7ac819 100644
--- a/cat_merge/merge_utils.py
+++ b/cat_merge/merge_utils.py
@@ -1,9 +1,8 @@
 import pandas as pd
 from pandas.core.frame import DataFrame
 from typing import List
-import os
 from cat_merge.model.merged_kg import MergedKG
-
+from cat_merge.mapping_utils import apply_mappings
 
 def concat_dataframes(dataframes: List[DataFrame]) -> DataFrame:
     return pd.concat(dataframes, axis=0)
@@ -31,11 +30,13 @@ def get_dangling_edges(edges: DataFrame, nodes: DataFrame) -> DataFrame:
     return edges[~edges.subject.isin(nodes.index) | ~edges.object.isin(nodes.index)]
 
 
-def merge_kg(edge_dfs: List[DataFrame], node_dfs: List[DataFrame], merge_delimiter: str = "|") -> MergedKG:
-
+def merge_kg(edge_dfs: List[DataFrame], node_dfs: List[DataFrame], mapping: DataFrame = None, merge_delimiter: str = "|") -> MergedKG:
     all_nodes = concat_dataframes(node_dfs)
     all_edges = concat_dataframes(edge_dfs)
 
+    if mapping is not None:
+        all_edges = apply_mappings(all_edges, mapping)
+
     duplicate_nodes = get_duplicate_rows(df=all_nodes)
     dangling_edges = get_dangling_edges(edges=all_edges, nodes=all_nodes)
 
diff --git a/tests/test_utils.py b/tests/test_utils.py
index b1ce976..88fb138 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -3,6 +3,9 @@
 
 
 # Borrowed from https://stackoverflow.com/questions/58771331/cleanly-hard-code-a-pandas-dataframe-into-a-python-script
-def string_df(data: str):
-    df = pd.read_csv(StringIO(data), index_col='id', sep=r"\s+", engine='python')
+def string_df(data: str, index_column_is_id=True):
+    if index_column_is_id:
+        df = pd.read_csv(StringIO(data), index_col='id', sep=r"\s+", engine='python')
+    else:
+        df = pd.read_csv(StringIO(data), sep=r"\s+", engine='python')
     return df
diff --git a/tests/unit/test_apply_mappings.py b/tests/unit/test_apply_mappings.py
new file mode 100644
index 0000000..806fd16
--- /dev/null
+++ b/tests/unit/test_apply_mappings.py
@@ -0,0 +1,46 @@
+import pytest
+from tests.test_utils import string_df
+from cat_merge.mapping_utils import apply_mappings
+
+@pytest.fixture
+def edges():
+    edges = u"""\
+    id      subject  object 
+    uuid:1  Gene:1   Disease:1 
+    uuid:2  XGene:2  Disease:2
+    uuid:3  Gene:2   XDisease:3
+    uuid:4  XGene:3  XDisease:4
+    """
+    return string_df(edges)
+
+
+@pytest.fixture
+def mapping():
+    mapping = u"""\
+    subject_id  object_id
+    XGene:1     Gene:1
+    XGene:2     Gene:2
+    XGene:3     Gene:3
+    XDisease:1  Disease:1
+    XDisease:2  Disease:2
+    XDisease:3  Disease:3
+    XDisease:4  Disease:4
+    """
+    return string_df(mapping, index_column_is_id=False)
+
+
+def test_apply_mappings(edges, mapping):
+    mapped_edges = apply_mappings(edges, mapping)
+
+    assert mapped_edges.loc['uuid:3']['subject'] == 'Gene:2'
+    assert mapped_edges.loc['uuid:3']['object'] == 'Disease:3'
+    assert mapped_edges.loc['uuid:4']['subject'] == 'Gene:3'
+    assert mapped_edges.loc['uuid:4']['object'] == 'Disease:4'
+
+
+def test_original_subject_and_object(edges, mapping):
+    mapped_edges = apply_mappings(edges, mapping)
+
+    assert mapped_edges.loc['uuid:2']['original_subject'] == 'XGene:2'
+    assert mapped_edges.loc['uuid:3']['original_object'] == 'XDisease:3'
+    assert mapped_edges.loc['uuid:4']['original_object'] == 'XDisease:4'