diff --git a/src/v0.1.0/entrytypes/structures.yaml b/src/v0.1.0/entrytypes/structures.yaml
index 0f2e6df..fb6e901 100644
--- a/src/v0.1.0/entrytypes/structures.yaml
+++ b/src/v0.1.0/entrytypes/structures.yaml
@@ -24,3 +24,11 @@ properties:
       sortable: true
       query-support: "all mandatory"
       response-level: "yes"
+
+  _cheminfo_inchikey:
+    $$inherit: "/properties/structures/_cheminfo_inchikey"
+    x-optimade-implementation:
+      support: "may"
+      sortable: false
+      query-support: "none"
+      response-level: "yes"
diff --git a/src/v0.1.0/properties/structures/_cheminfo_inchikey.yaml b/src/v0.1.0/properties/structures/_cheminfo_inchikey.yaml
new file mode 100644
index 0000000..968ca41
--- /dev/null
+++ b/src/v0.1.0/properties/structures/_cheminfo_inchikey.yaml
@@ -0,0 +1,19 @@
+$$schema: "https://schemas.optimade.org/meta/v1.2/optimade/property_definition"
+$id: "https://schemas.optimade.org/namespaces/cheminformatics/v0.1/properties/structures/_cheminfo_inchikey"
+title: "The standard InChIKey identifier of the structure, as laid out by the InChI Trust"
+x-optimade-type: "string"
+x-optimade-definition:
+  kind: "property"
+  version: "0.1.0"
+  format: "1.2"
+  name: "_cheminfo_inchikey"
+  label: "_cheminfo_inchikey_structures"
+type:
+  - "string"
+  - "null"
+description: |-
+  The standard InChIKey identifier of the structure, as laid out by the `InChI Trust (https://www.inchi-trust.org).
+  Standard InChIKey is non-unique, thus the same InChIKey can be assigned to several different structures.
+examples:
+  - "BQJCRHHNABKAKU-KBQPJGBKSA-N"
+x-optimade-unit: "inapplicable"