diff --git a/docs/api/countries.rst b/docs/api/countries.rst
index d60359f1..1c2b6fc8 100644
--- a/docs/api/countries.rst
+++ b/docs/api/countries.rst
@@ -33,6 +33,10 @@ and alpha-3 or alpha-2 codes, as shown in this example.
 
   from nomenclature import countries
 
+  # list of country names
+  countries.names
+
+  # mappings between ISO3 (alpha_3), alpha_2 and country names
   name = countries.get(alpha_3="...").name
   alpha_3 = countries.get(name="...").alpha_3
   alpha_2 = countries.get(name="...").alpha_2
diff --git a/nomenclature/code.py b/nomenclature/code.py
index 55ce3f00..097b6443 100644
--- a/nomenclature/code.py
+++ b/nomenclature/code.py
@@ -2,7 +2,7 @@
 import re
 from keyword import iskeyword
 from pathlib import Path
-from typing import Any, Dict, List, Set, Union
+from typing import Any, Dict, List, Set, Union, Optional
 from pydantic import (
     field_validator,
     field_serializer,
@@ -233,13 +233,28 @@ class RegionCode(Code):
         Name of the RegionCode
     hierarchy : str
         Hierarchy of the RegionCode
-    iso3_codes : str or list of str
+    countries : list of str, optional
+        List of countries in that region
+    iso3_codes : str or list of str, optional
         ISO3 codes of countries in that region
 
     """
 
     hierarchy: str = None
-    iso3_codes: Union[List[str], str] = None
+    countries: Optional[List[str]] = None
+    iso3_codes: Optional[Union[List[str], str]] = None
+
+    @field_validator("countries")
+    def check_countries(cls, v: List[str], info: ValidationInfo) -> List[str]:
+        """Verifies that each country name is defined in `nomenclature.countries`."""
+        if invalid_country_names := set(v) - set(countries.names):
+            raise ValueError(
+                f"Region '{info.data['name']}' uses non-standard country name(s): "
+                + ", ".join(invalid_country_names)
+                + "\nPlease use `nomenclature.countries` for consistency. (https://"
+                + "nomenclature-iamc.readthedocs.io/en/stable/api/countries.html)"
+            )
+        return v
 
     @field_validator("iso3_codes")
     def check_iso3_codes(cls, v: List[str], info: ValidationInfo) -> List[str]:
diff --git a/nomenclature/countries.py b/nomenclature/countries.py
index d7bfba81..7a191c5d 100644
--- a/nomenclature/countries.py
+++ b/nomenclature/countries.py
@@ -108,6 +108,10 @@ def get(self, **kwargs):
 
         return country
 
+    @property
+    def names(self):
+        return [country.name for country in self.objects]
+
 
 # Initialize `countries` for direct access via API and in codelist module
 countries = Countries()
diff --git a/tests/data/general-config-only/nomenclature.yaml b/tests/data/general-config-only/nomenclature.yaml
index 1c7e59e9..eb390c76 100644
--- a/tests/data/general-config-only/nomenclature.yaml
+++ b/tests/data/general-config-only/nomenclature.yaml
@@ -4,6 +4,5 @@ repositories:
 definitions:
   region:
     repository: common-definitions
-    country: true
   variable:
     repository: common-definitions
diff --git a/tests/data/general-config/nomenclature.yaml b/tests/data/general-config/nomenclature.yaml
index 644e304d..fe35a156 100644
--- a/tests/data/general-config/nomenclature.yaml
+++ b/tests/data/general-config/nomenclature.yaml
@@ -5,6 +5,5 @@ repositories:
 definitions:
   region:
     repository: common-definitions
-    country: true
   variable:
     repository: common-definitions
diff --git a/tests/data/region_codelist/countries_attribute_non-existing_name/region.yaml b/tests/data/region_codelist/countries_attribute_non-existing_name/region.yaml
new file mode 100644
index 00000000..15f969ed
--- /dev/null
+++ b/tests/data/region_codelist/countries_attribute_non-existing_name/region.yaml
@@ -0,0 +1,7 @@
+- common:
+  - World
+- countries:
+  - Some region:
+      # "Czech Republic" this was renamed to "Czechia" in ISO 3166-1 in 2023
+      countries: [ Austria, Germany, Czech Republic ]
+
diff --git a/tests/data/norway_as_bool/regions.yaml b/tests/data/region_codelist/norway_as_bool/region.yaml
similarity index 100%
rename from tests/data/norway_as_bool/regions.yaml
rename to tests/data/region_codelist/norway_as_bool/region.yaml
diff --git a/tests/data/region_codelist/region.yaml b/tests/data/region_codelist/simple/region.yaml
similarity index 100%
rename from tests/data/region_codelist/region.yaml
rename to tests/data/region_codelist/simple/region.yaml
diff --git a/tests/test_codelist.py b/tests/test_codelist.py
index 22b99dda..2d292fd7 100644
--- a/tests/test_codelist.py
+++ b/tests/test_codelist.py
@@ -147,7 +147,9 @@ def test_tags_in_list_attributes():
 
 def test_region_codelist():
     """Check replacing top-level hierarchy of yaml file as attribute for regions"""
-    code = RegionCodeList.from_directory("region", TEST_DATA_DIR / "region_codelist")
+    code = RegionCodeList.from_directory(
+        "region", TEST_DATA_DIR / "region_codelist" / "simple"
+    )
 
     assert "World" in code
     assert code["World"].hierarchy == "common"
@@ -157,9 +159,21 @@ def test_region_codelist():
     assert code["Some Country"].iso2 == "XY"
 
 
+def test_region_codelist_nonexisting_country_name():
+    """Check that countries are validated against `nomenclature.countries`"""
+    with pytest.raises(ValueError, match="Region 'Some region' .*: Czech Republic"):
+        RegionCodeList.from_directory(
+            "region",
+            TEST_DATA_DIR / "region_codelist" / "countries_attribute_non-existing_name",
+        )
+
+
 def test_norway_as_str():
     """guard against casting of 'NO' to boolean `False` by PyYAML or pydantic"""
-    region = RegionCodeList.from_directory("region", TEST_DATA_DIR / "norway_as_bool")
+    region = RegionCodeList.from_directory(
+        "region",
+        TEST_DATA_DIR / "region_codelist" / "norway_as_bool",
+    )
     assert region["Norway"].eu_member is False
     assert region["Norway"].iso2 == "NO"
 
diff --git a/tests/test_countries.py b/tests/test_countries.py
index eaff3e21..7d62e0b7 100644
--- a/tests/test_countries.py
+++ b/tests/test_countries.py
@@ -14,6 +14,8 @@ def test_countries_override(nc_name, iso_name, alpha_3):
     assert countries.get(name=iso_name).alpha_3 == "BOL"
     assert countries.get(alpha_3=alpha_3).name == nc_name
 
+    assert "Bolivia" in countries.names
+
 
 def test_countries_add():
     """Check that countries added to ISO 3166 can be found"""
@@ -23,6 +25,8 @@ def test_countries_add():
     with pytest.raises(AttributeError):
         countries.get(name="Kosovo").alpha_2
 
+    assert "Kosovo" in countries.names
+
 
 @pytest.mark.parametrize("alpha_2_eu, alpha_2", [("EL", "GR"), ("UK", "GB")])
 def test_alternative_alpha2(alpha_2_eu, alpha_2):
diff --git a/tests/test_definition.py b/tests/test_definition.py
index 5db19860..0f1d8cc1 100644
--- a/tests/test_definition.py
+++ b/tests/test_definition.py
@@ -51,12 +51,6 @@ def test_definition_from_general_config(workflow_folder):
             assert "Region A" in obs.region
         # imported from https://github.com/IAMconsortium/common-definitions repo
         assert "World" in obs.region
-        # added via general-config definitions
-        assert "Austria" in obs.region
-        # added via general-config definitions renamed from pycountry name
-        assert "Bolivia" in obs.region
-        # added via general-config definitions in addition to pycountry.countries
-        assert "Kosovo" in obs.region
 
         # imported from https://github.com/IAMconsortium/common-definitions repo
         assert "Primary Energy" in obs.variable