diff --git a/src/lenskit/data/builder.py b/src/lenskit/data/builder.py
index d891b3fce..6146755d4 100644
--- a/src/lenskit/data/builder.py
+++ b/src/lenskit/data/builder.py
@@ -265,10 +265,23 @@ def add_entities(
             duplicates:
                 How to handle duplicate entity IDs.
         """
-        if isinstance(source, pd.DataFrame):  # pragma: nocover
-            raise NotImplementedError()
-        if isinstance(source, pa.Table):  # pragma: nocover
-            raise NotImplementedError()
+        if isinstance(source, pd.DataFrame):
+            source = pa.Table.from_pandas(source)
+        if isinstance(source, pa.Table):
+            entity_col = source.column(cls + "_id")
+            self.add_entities(cls, entity_col)
+
+            for col_name in source.column_names:
+                if not col_name.endswith("_id"):
+                    col_type = source.column(col_name).type
+
+                    if any([pa.types.is_list(col_type), 
+                            pa.types.is_large_list(col_type), 
+                            pa.types.is_fixed_size_list(col_type)]):
+                        self.add_list_attribute(cls, col_name, entity_col, source.column(col_name))
+                    else:
+                        self.add_scalar_attribute(cls, col_name, entity_col, source.column(col_name))
+            return
 
         self._validate_entity_name(cls)
 
diff --git a/tests/data/test_builder_entities.py b/tests/data/test_builder_entities.py
index efbc039fa..93964b715 100644
--- a/tests/data/test_builder_entities.py
+++ b/tests/data/test_builder_entities.py
@@ -7,11 +7,13 @@
 # pyright: strict
 import numpy as np
 import pyarrow as pa
+import pandas as pd
 
 from pytest import raises
 
 from lenskit.data import DatasetBuilder
 from lenskit.diagnostics import DataError
+from lenskit.testing import ml_test_dir
 
 
 def test_empty_builder():
@@ -143,3 +145,38 @@ def test_add_entities_twice():
     assert ds.item_count == 0
     assert ds.user_count == 8
     assert np.all(ds.users.ids() == ["a", "b", "x", "y", "z", "q", "r", "s"])
+
+
+def test_add_entities_with_dataframe():
+    dsb = DatasetBuilder()
+
+    items = pd.read_csv(ml_test_dir / "movies.csv")
+    items = items.rename(columns={"movieId": "item_id"}).set_index("item_id")
+
+    genres = items["genres"].str.split("|")
+    items["genres"] = genres
+
+    dsb.add_entities("item", items)
+
+    ds = dsb.build()
+
+    assert ds.entities("item").attribute("title").is_scalar
+    assert ds.entities("item").attribute("genres").is_list
+
+
+def test_add_entities_with_arrow_table():
+    dsb = DatasetBuilder()
+
+    items = pd.read_csv(ml_test_dir / "movies.csv")
+    items = items.rename(columns={"movieId": "item_id"}).set_index("item_id")
+
+    genres = items["genres"].str.split("|")
+    items["genres"] = genres
+    table = pa.Table.from_pandas(items)
+
+    dsb.add_entities("item", table)
+
+    ds = dsb.build()
+
+    assert ds.entities("item").attribute("title").is_scalar
+    assert ds.entities("item").attribute("genres").is_list