diff --git a/stac_pydantic/item.py b/stac_pydantic/item.py
index 2f75f4c..4b2d54a 100644
--- a/stac_pydantic/item.py
+++ b/stac_pydantic/item.py
@@ -2,7 +2,6 @@
 
 from geojson_pydantic import Feature
 from pydantic import AnyUrl, ConfigDict, Field, model_serializer, model_validator
-from typing_extensions import Self
 
 from stac_pydantic.links import Links
 from stac_pydantic.shared import (
@@ -20,20 +19,12 @@ class ItemProperties(StacCommonMetadata):
     https://github.com/radiantearth/stac-spec/blob/v1.0.0/item-spec/item-spec.md#properties-object
     """
 
+    # Overide the datetime field to be required
     datetime: Optional[UtcDatetime]
 
     # Check https://docs.pydantic.dev/dev-v2/migration/#changes-to-config for more information.
     model_config = ConfigDict(extra="allow")
 
-    @model_validator(mode="after")
-    def validate_datetime(self) -> Self:
-        if not self.datetime and (not self.start_datetime or not self.end_datetime):
-            raise ValueError(
-                "start_datetime and end_datetime must be specified when datetime is null"
-            )
-
-        return self
-
 
 class Item(Feature, StacBaseModel):
     """
diff --git a/stac_pydantic/shared.py b/stac_pydantic/shared.py
index f06d6c0..126379b 100644
--- a/stac_pydantic/shared.py
+++ b/stac_pydantic/shared.py
@@ -9,8 +9,9 @@
     BaseModel,
     ConfigDict,
     Field,
+    model_validator,
 )
-from typing_extensions import Annotated
+from typing_extensions import Annotated, Self
 
 from stac_pydantic.utils import AutoValueEnum
 
@@ -126,22 +127,49 @@ class Provider(StacBaseModel):
 
 class StacCommonMetadata(StacBaseModel):
     """
-    https://github.com/radiantearth/stac-spec/blob/v1.0.0/item-spec/common-metadata.md#date-and-time-range
+    https://github.com/radiantearth/stac-spec/blob/v1.0.0/item-spec/common-metadata.md
     """
 
+    # Basic
     title: Optional[str] = None
     description: Optional[str] = None
-    start_datetime: Optional[UtcDatetime] = None
-    end_datetime: Optional[UtcDatetime] = None
+    # Date and Time
+    datetime: Optional[UtcDatetime] = None
     created: Optional[UtcDatetime] = None
     updated: Optional[UtcDatetime] = None
+    # Date and Time Range
+    start_datetime: Optional[UtcDatetime] = None
+    end_datetime: Optional[UtcDatetime] = None
+    # Provider
+    providers: Optional[List[Provider]] = None
+    # Instrument
     platform: Optional[str] = None
     instruments: Optional[List[str]] = None
     constellation: Optional[str] = None
     mission: Optional[str] = None
-    providers: Optional[List[Provider]] = None
     gsd: Optional[float] = Field(None, gt=0)
 
+    @model_validator(mode="after")
+    def validate_datetime_or_start_end(self) -> Self:
+        # When datetime is null, start_datetime and end_datetime must be specified
+        if not self.datetime and (not self.start_datetime or not self.end_datetime):
+            raise ValueError(
+                "start_datetime and end_datetime must be specified when datetime is null"
+            )
+
+        return self
+
+    @model_validator(mode="after")
+    def validate_start_end(self) -> Self:
+        # Using one of start_datetime or end_datetime requires the use of the other
+        if (self.start_datetime and not self.end_datetime) or (
+            not self.start_datetime and self.end_datetime
+        ):
+            raise ValueError(
+                "use of start_datetime or end_datetime requires the use of the other"
+            )
+        return self
+
 
 class Asset(StacCommonMetadata):
     """
@@ -157,3 +185,10 @@ class Asset(StacCommonMetadata):
     model_config = ConfigDict(
         populate_by_name=True, use_enum_values=True, extra="allow"
     )
+
+    @model_validator(mode="after")
+    def validate_datetime_or_start_end(self) -> Self:
+        # Overriding the parent method to avoid requiring datetime or start/end_datetime
+        # Additional fields MAY be added on the Asset object, but are not required.
+        # https://github.com/radiantearth/stac-spec/blob/v1.0.0/item-spec/item-spec.md#additional-fields-for-assets
+        return self
diff --git a/tests/test_models.py b/tests/test_models.py
index fc348db..6472bee 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -8,7 +8,7 @@
 from stac_pydantic import Collection, Item, ItemProperties
 from stac_pydantic.extensions import validate_extensions
 from stac_pydantic.links import Link, Links
-from stac_pydantic.shared import MimeTypes
+from stac_pydantic.shared import MimeTypes, StacCommonMetadata
 
 from .conftest import dict_match, request
 
@@ -169,10 +169,15 @@ def test_geo_interface() -> None:
             "start_datetime": "2024-01-01T00:00:00Z",
             "end_datetime": "2024-01-02T00:00:00Z",
         },
+        {
+            "datetime": "2024-01-01T00:00:00Z",
+            "start_datetime": "2024-01-01T00:00:00Z",
+            "end_datetime": "2024-01-02T00:00:00Z",
+        },
     ],
 )
-def test_item_properties_dates(args) -> None:
-    ItemProperties(**args)
+def test_stac_common_dates(args) -> None:
+    StacCommonMetadata(**args)
 
 
 @pytest.mark.parametrize(
@@ -183,12 +188,27 @@ def test_item_properties_dates(args) -> None:
         {"datetime": None, "end_datetime": "2024-01-01T00:00:00Z"},
     ],
 )
-def test_item_properties_no_dates(args) -> None:
+def test_stac_common_no_dates(args) -> None:
     with pytest.raises(
         ValueError,
         match="start_datetime and end_datetime must be specified when datetime is null",
     ):
-        ItemProperties(**args)
+        StacCommonMetadata(**args)
+
+
+@pytest.mark.parametrize(
+    "args",
+    [
+        {"datetime": "2024-01-01T00:00:00Z", "start_datetime": "2024-01-01T00:00:00Z"},
+        {"datetime": "2024-01-01T00:00:00Z", "end_datetime": "2024-01-01T00:00:00Z"},
+    ],
+)
+def test_stac_common_start_and_end(args) -> None:
+    with pytest.raises(
+        ValueError,
+        match="use of start_datetime or end_datetime requires the use of the other",
+    ):
+        StacCommonMetadata(**args)
 
 
 def test_declared_model() -> None: