diff --git a/README.rst b/README.rst
index c207324d..82c8e4ba 100644
--- a/README.rst
+++ b/README.rst
@@ -82,7 +82,7 @@ Besides the numerical argument, there are two main optional arguments, ``to:`` a
 * ``be`` (Belarusian)
 * ``ce`` (Chechen)
 * ``cy`` (Welsh)
-* ``cz`` (Czech)
+* ``cs`` (Czech)
 * ``de`` (German)
 * ``dk`` (Danish)
 * ``en_GB`` (English - Great Britain)
diff --git a/num2words/__init__.py b/num2words/__init__.py
index c513d853..934e09ff 100644
--- a/num2words/__init__.py
+++ b/num2words/__init__.py
@@ -18,7 +18,7 @@
 from __future__ import unicode_literals
 
 from . import (lang_AM, lang_AR, lang_AZ, lang_BE, lang_CA, lang_CE, lang_CY,
-               lang_CZ, lang_DE, lang_DK, lang_EN, lang_EN_IN, lang_EN_NG,
+               lang_CS, lang_DE, lang_DK, lang_EN, lang_EN_IN, lang_EN_NG,
                lang_EO, lang_ES, lang_ES_CO, lang_ES_CR, lang_ES_GT,
                lang_ES_NI, lang_ES_VE, lang_FA, lang_FI, lang_FR, lang_FR_BE,
                lang_FR_CH, lang_FR_DZ, lang_HE, lang_HU, lang_ID, lang_IS,
@@ -34,8 +34,8 @@
     'be': lang_BE.Num2Word_BE(),
     'ca': lang_CA.Num2Word_CA(),
     'ce': lang_CE.Num2Word_CE(),
+    'cs': lang_CS.Num2Word_CS(),
     'cy': lang_CY.Num2Word_CY(),
-    'cz': lang_CZ.Num2Word_CZ(),
     'en': lang_EN.Num2Word_EN(),
     'en_IN': lang_EN_IN.Num2Word_EN_IN(),
     'en_NG': lang_EN_NG.Num2Word_EN_NG(),
diff --git a/num2words/lang_CZ.py b/num2words/lang_CS.py
similarity index 99%
rename from num2words/lang_CZ.py
rename to num2words/lang_CS.py
index 04c44a07..6024b77d 100644
--- a/num2words/lang_CZ.py
+++ b/num2words/lang_CS.py
@@ -84,7 +84,7 @@
 }
 
 
-class Num2Word_CZ(Num2Word_Base):
+class Num2Word_CS(Num2Word_Base):
     CURRENCY_FORMS = {
         'CZK': (
             ('koruna', 'koruny', 'korun'), ('halíř', 'halíře', 'haléřů')
diff --git a/tests/test_cz.py b/tests/test_cs.py
similarity index 72%
rename from tests/test_cz.py
rename to tests/test_cs.py
index 1801e8f7..2c2b0e5f 100644
--- a/tests/test_cz.py
+++ b/tests/test_cs.py
@@ -22,39 +22,39 @@
 from num2words import num2words
 
 
-class Num2WordsCZTest(TestCase):
+class Num2WordsCSTest(TestCase):
     def test_cardinal(self):
-        self.assertEqual(num2words(100, lang='cz'), "sto")
-        self.assertEqual(num2words(101, lang='cz'), "sto jedna")
-        self.assertEqual(num2words(110, lang='cz'), "sto deset")
-        self.assertEqual(num2words(115, lang='cz'), "sto patnáct")
-        self.assertEqual(num2words(123, lang='cz'), "sto dvacet tři")
-        self.assertEqual(num2words(1000, lang='cz'), "tisíc")
-        self.assertEqual(num2words(1001, lang='cz'), "tisíc jedna")
-        self.assertEqual(num2words(2012, lang='cz'), "dva tisíce dvanáct")
-        self.assertEqual(
-            num2words(10.02, lang='cz'),
+        self.assertEqual(num2words(100, lang='cs'), "sto")
+        self.assertEqual(num2words(101, lang='cs'), "sto jedna")
+        self.assertEqual(num2words(110, lang='cs'), "sto deset")
+        self.assertEqual(num2words(115, lang='cs'), "sto patnáct")
+        self.assertEqual(num2words(123, lang='cs'), "sto dvacet tři")
+        self.assertEqual(num2words(1000, lang='cs'), "tisíc")
+        self.assertEqual(num2words(1001, lang='cs'), "tisíc jedna")
+        self.assertEqual(num2words(2012, lang='cs'), "dva tisíce dvanáct")
+        self.assertEqual(
+            num2words(10.02, lang='cs'),
             "deset celá nula dva"
         )
         self.assertEqual(
-            num2words(15.007, lang='cz'),
+            num2words(15.007, lang='cs'),
             "patnáct celá nula nula sedm"
         )
         self.assertEqual(
-            num2words(12519.85, lang='cz'),
+            num2words(12519.85, lang='cs'),
             "dvanáct tisíc pětset devatenáct celá osmdesát pět"
         )
         self.assertEqual(
-            num2words(123.50, lang='cz'),
+            num2words(123.50, lang='cs'),
             "sto dvacet tři celá pět"
         )
         self.assertEqual(
-            num2words(1234567890, lang='cz'),
+            num2words(1234567890, lang='cs'),
             "miliarda dvěstě třicet čtyři miliony pětset šedesát "
             "sedm tisíc osmset devadesát"
         )
         self.assertEqual(
-            num2words(215461407892039002157189883901676, lang='cz'),
+            num2words(215461407892039002157189883901676, lang='cs'),
             "dvěstě patnáct quintillionů čtyřista šedesát jedna kvadriliard "
             "čtyřista sedm kvadrilionů osmset devadesát dva triliardy třicet "
             "devět trilionů dva biliardy sto padesát sedm bilionů sto "
@@ -62,7 +62,7 @@ def test_cardinal(self):
             "devětset jedna tisíc šestset sedmdesát šest"
         )
         self.assertEqual(
-            num2words(719094234693663034822824384220291, lang='cz'),
+            num2words(719094234693663034822824384220291, lang='cs'),
             "sedmset devatenáct quintillionů devadesát "
             "čtyři kvadriliardy dvěstě třicet čtyři "
             "kvadriliony šestset devadesát tři triliardy "
@@ -75,40 +75,40 @@ def test_cardinal(self):
     def test_to_ordinal(self):
         # @TODO: implement to_ordinal
         with self.assertRaises(NotImplementedError):
-            num2words(1, lang='cz', to='ordinal')
+            num2words(1, lang='cs', to='ordinal')
 
     def test_currency(self):
         self.assertEqual(
-            num2words(10.0, lang='cz', to='currency', currency='EUR'),
+            num2words(10.0, lang='cs', to='currency', currency='EUR'),
             "deset euro, nula centů")
         self.assertEqual(
-            num2words(1.0, lang='cz', to='currency', currency='CZK'),
+            num2words(1.0, lang='cs', to='currency', currency='CZK'),
             "jedna koruna, nula haléřů")
         self.assertEqual(
-            num2words(1234.56, lang='cz', to='currency', currency='EUR'),
+            num2words(1234.56, lang='cs', to='currency', currency='EUR'),
             "tisíc dvěstě třicet čtyři euro, padesát šest centů")
         self.assertEqual(
-            num2words(1234.56, lang='cz', to='currency', currency='CZK'),
+            num2words(1234.56, lang='cs', to='currency', currency='CZK'),
             "tisíc dvěstě třicet čtyři koruny, padesát šest haléřů")
         self.assertEqual(
-            num2words(101.11, lang='cz', to='currency', currency='EUR',
+            num2words(101.11, lang='cs', to='currency', currency='EUR',
                       separator=' a'),
             "sto jedna euro a jedenáct centů")
         self.assertEqual(
-            num2words(101.21, lang='cz', to='currency', currency='CZK',
+            num2words(101.21, lang='cs', to='currency', currency='CZK',
                       separator=' a'),
             "sto jedna korun a dvacet jedna haléřů"
         )
         self.assertEqual(
-            num2words(-12519.85, lang='cz', to='currency', cents=False),
+            num2words(-12519.85, lang='cs', to='currency', cents=False),
             "mínus dvanáct tisíc pětset devatenáct euro, 85 centů"
         )
         self.assertEqual(
-            num2words(123.50, lang='cz', to='currency', currency='CZK',
+            num2words(123.50, lang='cs', to='currency', currency='CZK',
                       separator=' a'),
             "sto dvacet tři koruny a padesát haléřů"
         )
         self.assertEqual(
-            num2words(19.50, lang='cz', to='currency', cents=False),
+            num2words(19.50, lang='cs', to='currency', cents=False),
             "devatenáct euro, 50 centů"
         )