diff --git a/optimade.rst b/optimade.rst
index 2947c3fcf..97ba5d3b1 100644
--- a/optimade.rst
+++ b/optimade.rst
@@ -2500,6 +2500,21 @@ chemical\_formula\_anonymous
 
   - A filter that matches an exactly given formula is :filter:`chemical_formula_anonymous="A2B"`.
 
+inchikey
+~~~~~~~~
+
+- **Description**: The standard InChIKey identifier of the structure, as laid out by the `InChI Trust <https://www.inchi-trust.org>`_.
+  Standard InChIKey is not guaranteed to be unique and in extremely rare cases the same InChIKey may be assigned to several different structures.
+- **Type**: string
+- **Requirements/Conventions**:
+
+  - **Support**: OPTIONAL support in implementations, i.e., MAY be :val:`null`.
+  - **Query**: Support for queries on this property is OPTIONAL.
+
+- **Examples**:
+
+  - Morphine: :val:`BQJCRHHNABKAKU-KBQPJGBKSA-N`
+
 dimension\_types
 ~~~~~~~~~~~~~~~~