diff --git a/openmc/data/njoy.py b/openmc/data/njoy.py
new file mode 100644
index 000000000..3dee4259f
--- /dev/null
+++ b/openmc/data/njoy.py
@@ -0,0 +1,301 @@
+#!/usr/bin/env python
+
+import argparse
+from collections import namedtuple
+from io import StringIO
+import os
+import shutil
+from subprocess import run, PIPE, STDOUT
+import sys
+import tempfile
+
+import openmc.data
+
+_NJOY_2012 = False
+
+# For a given MAT number, give a name for the ACE table and a list of ZAID
+# identifiers
+ThermalTuple = namedtuple('ThermalTuple', ['name', 'zaids', 'nmix'])
+_THERMAL_DATA = {
+    1: ThermalTuple('hh2o', [1001], 1),
+    2: ThermalTuple('parah', [1001], 1),
+    3: ThermalTuple('orthoh', [1001], 1),
+    5: ThermalTuple('hyh2', [1001], 1),
+    7: ThermalTuple('hzrh', [1001], 1),
+    8: ThermalTuple('hcah2', [1001], 1),
+    10: ThermalTuple('hice', [1001], 1),
+    11: ThermalTuple('dd2o', [1002], 1),
+    12: ThermalTuple('parad', [1002], 1),
+    13: ThermalTuple('orthod', [1002], 1),
+    26: ThermalTuple('be', [4009], 1),
+    27: ThermalTuple('bebeo', [4009], 1),
+    31: ThermalTuple('graph', [6000, 6012, 6013], 1),
+    33: ThermalTuple('lch4', [1001], 1),
+    34: ThermalTuple('sch4', [1001], 1),
+    37: ThermalTuple('hch2', [1001], 1),
+    39: ThermalTuple('lucite', [1001], 1),
+    40: ThermalTuple('benz', [1001, 6000, 6012], 2),
+    41: ThermalTuple('od2o', [8016, 8017, 8018], 1),
+    43: ThermalTuple('sisic', [14028, 14029, 14030], 1),
+    44: ThermalTuple('csic', [6000, 6012, 6013], 1),
+    46: ThermalTuple('obeo', [8016, 8017, 8018], 1),
+    47: ThermalTuple('sio2-a', [8016, 8017, 8018, 14028, 14029, 14030], 3),
+    48: ThermalTuple('uuo2', [92238], 1),
+    49: ThermalTuple('sio2-b', [8016, 8017, 8018, 14028, 14029, 14030], 3),
+    50: ThermalTuple('oice', [8016, 8017, 8018], 1),
+    52: ThermalTuple('mg24', [12024], 1),
+    53: ThermalTuple('al27', [13027], 1),
+    55: ThermalTuple('yyh2', [39089], 1),
+    56: ThermalTuple('fe56', [26056], 1),
+    58: ThermalTuple('zrzrh', [40000, 40090, 40091, 40092, 40094, 40096], 1),
+    59: ThermalTuple('cacah2', [20040, 20042, 20043, 20044, 20046, 20048], 1),
+    75: ThermalTuple('ouo2', [8016, 8017, 8018], 1),
+}
+
+
+_PENDF_TEMPLATE = """
+reconr / %%%%%%%%%%%%%%%%%%% Reconstruct XS for neutrons %%%%%%%%%%%%%%%%%%%%%%%
+20 22
+'{library} PENDF for {zsymam}'/
+{mat} 2/
+0.001 0.0 0.003/ err tempr errmax
+'{library}: {zsymam}'/
+'Processed by NJOY2012.50'/
+0/
+stop
+"""
+
+_ACE_TEMPLATE = """
+reconr / %%%%%%%%%%%%%%%%%%% Reconstruct XS for neutrons %%%%%%%%%%%%%%%%%%%%%%%
+20 21
+'{library} PENDF for {zsymam}'/
+{mat} 2/
+0.001 0.0 0.003/ err tempr errmax
+'{library}: {zsymam}'/
+'Processed by NJOY2012.50'/
+0/
+broadr / %%%%%%%%%%%%%%%%%%%%%%% Doppler broaden XS %%%%%%%%%%%%%%%%%%%%%%%%%%%%
+20 21 22
+{mat} 1 0 0 0. /
+0.001 -1.0e6 0.003 /
+293.6
+0/
+heatr / %%%%%%%%%%%%%%%%%%%%%%%%% Add heating kerma %%%%%%%%%%%%%%%%%%%%%%%%%%%%
+20 22 23 /
+{mat} {num_partials} /
+{heatr_partials} /
+purr / %%%%%%%%%%%%%%%%%%%%%%%% Add probability tables %%%%%%%%%%%%%%%%%%%%%%%%%
+20 23 24
+{mat} 1 5 20 64 /
+293.6
+1.e10 1.e4 1.e3 1.e2 1.e1
+0/
+acer / %%%%%%%%%%%%%%%%%%%%%%%%%%%%% Make ACE file %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+20 24 0 25 26
+1 0 1 .01 /
+'{library}: {zsymam} processed by NJOY2012.50'/
+{mat} 293.6
+1 1/
+/
+stop
+"""
+
+_ACE_THERMAL_TEMPLATE = """
+reconr / %%%%%%%%%%%%%%%%%%% Reconstruct XS for neutrons %%%%%%%%%%%%%%%%%%%%%%%
+20 22
+'{library} PENDF for {zsymam}'/
+{mat} 2/
+0.001 0. 0.001/ err tempr errmax
+'{library}: PENDF for {zsymam}'/
+'Processed by NJOY2012.50'/
+0/
+broadr / %%%%%%%%%%%%%%%%%%%%%%% Doppler broaden XS %%%%%%%%%%%%%%%%%%%%%%%%%%%%
+20 22 23
+{mat} 1 0 0 0./
+0.001 2.0e+6 0.001/ errthn thnmax errmax
+{temperature}
+0/
+thermr / %%%%%%%%%%%%%%%% Add thermal scattering data (free gas) %%%%%%%%%%%%%%%
+0 23 62
+0 {mat} 12 1 1 0 {iform} 1 221 1/
+{temperature}
+0.001 4.0
+thermr / %%%%%%%%%%%%%%%% Add thermal scattering data (bound) %%%%%%%%%%%%%%%%%%
+60 62 27
+{mat_thermal} {mat} 16 1 {inelastic} {elastic} {iform} {natom} 222 1/
+{temperature}
+0.001 4.0
+acer / %%%%%%%%%%%%%%%%%%%%%%%%%%%%% Make ACE file %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+20 27 0 28 29
+2 0 1 .01/
+'{library}: {zsymam_thermal} processed by NJOY2012.50'/
+{mat} {temperature} '{data.name}' /
+{zaids} /
+222 64 {mt_elastic} {elastic_type} {data.nmix} {energy_max} 2/
+stop
+"""
+
+def make_pendf(filename, output=None):
+    ev = openmc.data.endf.Evaluation(filename)
+    mat = ev.material
+    zsymam = ev.target['zsymam']
+
+    # Determine name of library
+    library = '{}-{}.{}'.format(*ev.info['library'])
+
+    with tempfile.TemporaryDirectory() as tmpdirname:
+        # Copy evaluation to tape20
+        shutil.copy(filename, os.path.join(tmpdirname, 'tape20'))
+
+        commands = _PENDF_TEMPLATE.format(**locals())
+        njoy = run(['njoy'], cwd=tmpdirname, input=commands, stdout=PIPE,
+                   stderr=STDOUT, universal_newlines=True)
+        if njoy.returncode != 0:
+            print('Failed to produce PENDF for {}'.format(filename))
+
+        if output is None:
+            output = zsymam.replace(' ', '') + '.pendf'
+
+        pendf_file = os.path.join(tmpdirname, 'tape22')
+        if os.path.isfile(pendf_file):
+            shutil.move(pendf_file, output)
+
+    return njoy
+
+
+def make_ace(filename, output=None):
+    ev = openmc.data.endf.Evaluation(filename)
+    mat = ev.material
+    zsymam = ev.target['zsymam']
+
+    with tempfile.TemporaryDirectory() as tmpdirname:
+        # Copy evaluation to tape20
+        shutil.copy(filename, os.path.join(tmpdirname, 'tape20'))
+
+        # Determine which partial heating values are needed to self-shield heating
+        # for ptables
+        partials = [302, 402]
+        if ev.target['fissionable']:
+            partials.append(318)
+        heatr_partials = ' '.join(map(str, partials))
+        num_partials = len(partials)
+
+        commands = _ACE_TEMPLATE.format(**locals())
+        njoy = run(['njoy'], cwd=tmpdirname, input=commands, stdout=PIPE,
+                   stderr=STDOUT, universal_newlines=True)
+        if njoy.returncode != 0:
+            print('Failed to produce ACE for {}'.format(filename))
+
+        if output is None:
+            output = zsymam.replace(' ', '') + '.ace'
+        output_xsdir = zsymam.replace(' ', '') + '.xsdir'
+        output_njoy = zsymam.replace(' ', '') + '.output'
+
+        ace_file = os.path.join(tmpdirname, 'tape25')
+        xsdir_file = os.path.join(tmpdirname, 'tape26')
+        output_file = os.path.join(tmpdirname, 'output')
+        if os.path.exists(ace_file):
+            shutil.move(ace_file, output)
+        if os.path.exists(xsdir_file):
+            shutil.move(xsdir_file, output_xsdir)
+        if os.path.exists(output_file):
+            shutil.move(output_file, output_njoy)
+        shutil.move(os.path.join(tmpdirname, 'tape21'), 'pendf')
+
+    # Write NJOY output
+    open(zsymam.replace(' ', '') + '.njo', 'w').write(njoy.stdout)
+
+    # If the target is metastable, make sure that ZAID in the ACE file reflects
+    # this by adding 400
+    if ev.target['isomeric_state'] > 0:
+        text = open(output, 'r').read()
+        mass_first_digit = int(text[3])
+        if mass_first_digit <= 2:
+            print('    Fixing {} (metastable ZAID)...'.format(output))
+            text = text[:3] + str(mass_first_digit + 4) + text[4:]
+            open(output, 'w').write(text)
+
+    return njoy
+
+
+def make_ace_thermal(filename, filename_thermal, temperature, output=None):
+    ev = openmc.data.endf.Evaluation(filename)
+    mat = ev.material
+    zsymam = ev.target['zsymam']
+
+    ev_thermal = openmc.data.endf.Evaluation(filename_thermal)
+    mat_thermal = ev_thermal.material
+    zsymam_thermal = ev_thermal.target['zsymam']
+
+    data = _THERMAL_DATA[mat_thermal]
+    zaids = ' '.join(str(zaid) for zaid in data.zaids[:3])
+    energy_max = ev_thermal.info['energy_max']
+
+    # Determine name of library
+    library = '{}-{}.{}'.format(*ev_thermal.info['library'])
+
+    # Determine if thermal elastic is present
+    if (7, 2) in ev_thermal.section:
+        elastic = 1
+        mt_elastic = 223
+
+        # Determine whether elastic is incoherent (0) or coherent (1)
+        file_obj = StringIO(ev_thermal.section[7, 2])
+        elastic_type = openmc.data.endf.get_head_record(file_obj)[2]
+    else:
+        elastic = 0
+        mt_elastic = 0
+        elastic_type = 0
+
+    # Determine number of principal atoms
+    file_obj = StringIO(ev_thermal.section[7, 4])
+    items = openmc.data.endf.get_head_record(file_obj)
+    items, values = openmc.data.endf.get_list_record(file_obj)
+    natom = int(values[5])
+
+    # A few parameters are different in NJOY 99 and NJOY 2012
+    if _NJOY_2012:
+        iform = 0
+        inelastic = 2
+    else:
+        iform = ''
+        inelastic = 4
+
+    with tempfile.TemporaryDirectory() as tmpdirname:
+        # Copy evaluation to tape20
+        shutil.copy(filename, os.path.join(tmpdirname, 'tape20'))
+        shutil.copy(filename_thermal, os.path.join(tmpdirname, 'tape60'))
+
+        commands = _ACE_THERMAL_TEMPLATE.format(**locals())
+        njoy = run(['njoy'], cwd=tmpdirname, input=commands, stdout=PIPE,
+                   stderr=STDOUT, universal_newlines=True)
+        if njoy.returncode != 0:
+            print('Failed to produce ACE for {}'.format(filename_thermal))
+
+        if output is None:
+            output = data.name + '.ace'
+        output_xsdir = data.name + '.xsdir'
+        output_njoy = data.name + '.output'
+
+        ace_file = os.path.join(tmpdirname, 'tape28')
+        xsdir_file = os.path.join(tmpdirname, 'tape29')
+        output_file = os.path.join(tmpdirname, 'output')
+        if os.path.exists(ace_file):
+            shutil.move(ace_file, output)
+        if os.path.exists(xsdir_file):
+            shutil.move(xsdir_file, output_xsdir)
+        if os.path.exists(output_file):
+            shutil.move(output_file, output_njoy)
+
+    # Write NJOY output
+    open(data.name + '.njo', 'w').write(njoy.stdout)
+
+    return njoy
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filename', help='Path to ENDF file')
+    args = parser.parse_args()
+
+    make_ace(args.filename)