diff --git a/mesa-to-castro-format.py b/mesa-to-castro-format.py
new file mode 100644
index 0000000..0bee3e9
--- /dev/null
+++ b/mesa-to-castro-format.py
@@ -0,0 +1,80 @@
+import numpy as np
+import argparse
+
+'''
+This script turns a file in MESA's log file format:
+                           1                            2
+                model_number                    num_zones
+                       13700                         4055
+
+                           1                            2
+                          dm                            q
+     1.6956238372097480E+022      1.0000000000000000E+000
+     1.6956238372097480E+022      9.9999999999949996E-001
+
+into Castro's new format:
+# radius density temperature
+        0.1           3         4.0
+        0.2           4         3.9
+        0.3           4         3.7
+'''
+
+
+def main(file_name, new_file_name):
+    # read in MESA file
+    bulk_data = np.genfromtxt(
+        file_name,
+        skip_header=5,
+        names=True,
+        ndmin=1,
+        dtype=None,
+    )
+    bulk_names = bulk_data.dtype.names
+
+    # identify needed columns and their aliases
+    variable_names = {
+        "radius": "radius_cm",
+        "density": "density",
+        "temperature": "temperature",
+        "ye": "ye",
+        "velx": "velocity",
+        "pressure": "pressure",
+        "entr": "entropy",
+        "abar": "abar",
+        "enuc": "eps_nuc"
+    } # castro column name: mesa column name
+    
+    # add in the composition columns:
+    # found in the range [neutron, opacity)
+    neutron_name = {'n', 'neut', 'neutron'}.intersection(bulk_names)
+    if len(neutron_name) < 1:
+        raise ValueError("No 'n', 'neut', or 'neutron' in MESA file column names.")
+    start = bulk_names.index(neutron_name.pop())
+    end = bulk_names.index('opacity')
+
+    # set up new columns
+    col_names = list(variable_names.keys()) + list(bulk_names[start:end])
+    associated_indices = [bulk_names.index(v) for v in variable_names.values()] + list(range(start, end))
+
+    # write new columns to new file
+    with open(new_file_name, 'w') as f:
+        f.write(f"# {' '.join(col_names)}\n")
+        for row in bulk_data:
+            row = list(row)
+            display_row = [str(row[i]).rjust(30) for i in associated_indices]
+            f.write(f'{"".join(display_row)}\n')
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="Reformat a 1D model file from MESA's output format to Castro's preferred input format.")
+    parser.add_argument('file_name')
+    parser.add_argument('new_file_name', nargs='?')
+    args = parser.parse_args()
+    if args.new_file_name is None:
+        file_stem, file_ending = args.file_name.rsplit('.',1)
+        new_file_name = f"{file_stem}.castro.{file_ending}"
+    else:
+        new_file_name = args.new_file_name
+    main(args.file_name, new_file_name)
+
+    print('Saved new Castro-readable file in', new_file_name)