diff --git a/spec/API_specification/dataframe_api/dataframe_object.py b/spec/API_specification/dataframe_api/dataframe_object.py
index 7de9d006..95bc288c 100644
--- a/spec/API_specification/dataframe_api/dataframe_object.py
+++ b/spec/API_specification/dataframe_api/dataframe_object.py
@@ -11,6 +11,15 @@
 
 
 class DataFrame:
+    @property
+    def dataframe(self) -> object:
+        """
+        Return underlying (not-necessarily-Standard-compliant) DataFrame.
+
+        If a library only implements the Standard, then this can return `self`.
+        """
+        ...
+
     def groupby(self, keys: Sequence[str], /) -> GroupBy:
         """
         Group the DataFrame by the given columns.