diff --git a/spec/Section 3 -- Type System.md b/spec/Section 3 -- Type System.md
index 6941e20d8..7f974a90b 100644
--- a/spec/Section 3 -- Type System.md	
+++ b/spec/Section 3 -- Type System.md	
@@ -755,6 +755,28 @@ Union types have the potential to be invalid if incorrectly defined.
    Similarly, wrapping types may not be member types of a Union.
 2. A Union type must define one or more unique member types.
 
+#### Union type syntax
+
+Union types are defined by delimiting one or more types with a single vertical bar character `|`:
+
+```graphql
+union SearchResult = Photo | Person
+```
+
+You may also use a leading vertical bar:
+
+```graphql
+union SearchResult =
+  | Photo
+  | Person
+```
+
+Trailing delimiters are not supported:
+
+```!graphql
+union SearchResult = Photo | Person |
+```
+
 ### Enums
 
 GraphQL Enums are a variant on the Scalar type, which represents one of a