diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3462d023..773cea20 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Clarified that trailing slashes in URIs are significant. ([#1212](https://github.com/radiantearth/stac-spec/discussions/1212))
 - All JSON Schema `$id` values no longer have `#` at the end.
 - Two spatial bounding boxes in a Collection don't make sense and will be reported as invalid by the schema. ([#1243](https://github.com/radiantearth/stac-spec/issues/1243))
+- Clarify in descriptions that start_datetime and end_datetime are inclusive bounds ([#1280](https://github.com/radiantearth/stac-spec/issues/1280))
 
 ### Deprecated
 
diff --git a/item-spec/common-metadata.md b/item-spec/common-metadata.md
index 5ebdb53a..1d54f8f9 100644
--- a/item-spec/common-metadata.md
+++ b/item-spec/common-metadata.md
@@ -78,6 +78,9 @@ The datetime property in a STAC Item and these fields are not mutually exclusive
 | start_datetime | string | The first or start date and time for the resource, in UTC. It is formatted as `date-time` according to [RFC 3339, section 5.6](https://tools.ietf.org/html/rfc3339#section-5.6). |
 | end_datetime   | string | The last or end date and time for the resource, in UTC. It is formatted as `date-time` according to [RFC 3339, section 5.6](https://tools.ietf.org/html/rfc3339#section-5.6).    |
 
+`start_datetime` and `end_datetime` constitute inclusive bounds,
+meaning that the range covers the entire time interval between the two timestamps and the timestamps itself.
+
 ## Licensing
 
 Information about the license(s) of the data, which is not necessarily the same license that applies to the metadata.