diff --git a/cxxheaderparser/parser.py b/cxxheaderparser/parser.py
index 56a893f..f6ecdbc 100644
--- a/cxxheaderparser/parser.py
+++ b/cxxheaderparser/parser.py
@@ -35,6 +35,7 @@ from .types import (
     Method,
     MoveReference,
     NameSpecifier,
+    NamespaceAlias,
     NamespaceDecl,
     Operator,
     PQNameSegment,
@@ -404,13 +405,26 @@ class CxxParser:
 
         names = []
         location = tok.location
+        ns_alias: typing.Union[typing.Literal[False], LexToken] = False
 
         tok = self._next_token_must_be("NAME", "{")
         if tok.type != "{":
+            endtok = "{"
+            # Check for namespace alias here
+            etok = self.lex.token_if("=")
+            if etok:
+                ns_alias = tok
+                endtok = ";"
+                # They can start with ::
+                maybe_tok = self.lex.token_if("DBL_COLON")
+                if maybe_tok:
+                    names.append(maybe_tok.value)
+                tok = self._next_token_must_be("NAME")
+
             while True:
                 names.append(tok.value)
-                tok = self._next_token_must_be("DBL_COLON", "{")
-                if tok.type == "{":
+                tok = self._next_token_must_be("DBL_COLON", endtok)
+                if tok.type == endtok:
                     break
 
                 tok = self._next_token_must_be("NAME")
@@ -418,7 +432,10 @@ class CxxParser:
         if inline and len(names) > 1:
             raise CxxParseError("a nested namespace definition cannot be inline")
 
-        # TODO: namespace_alias_definition
+        if ns_alias:
+            alias = NamespaceAlias(ns_alias.value, names)
+            self.visitor.on_namespace_alias(self.state, alias)
+            return
 
         ns = NamespaceDecl(names, inline, doxygen)
         state = self._push_state(NamespaceBlockState, ns)
diff --git a/cxxheaderparser/simple.py b/cxxheaderparser/simple.py
index ea34c66..65cf04a 100644
--- a/cxxheaderparser/simple.py
+++ b/cxxheaderparser/simple.py
@@ -39,6 +39,7 @@ from .types import (
     FriendDecl,
     Function,
     Method,
+    NamespaceAlias,
     TemplateInst,
     Typedef,
     UsingAlias,
@@ -110,6 +111,7 @@ class NamespaceScope:
     using: typing.List[UsingDecl] = field(default_factory=list)
     using_ns: typing.List["UsingNamespace"] = field(default_factory=list)
     using_alias: typing.List[UsingAlias] = field(default_factory=list)
+    ns_alias: typing.List[NamespaceAlias] = field(default_factory=list)
 
     #: Explicit template instantiations
     template_insts: typing.List[TemplateInst] = field(default_factory=list)
@@ -261,6 +263,10 @@ class SimpleCxxVisitor:
         self.block = self.block_stack.pop()
         self.namespace = self.ns_stack.pop()
 
+    def on_namespace_alias(self, state: State, alias: NamespaceAlias) -> None:
+        assert isinstance(self.block, NamespaceScope)
+        self.block.ns_alias.append(alias)
+
     def on_forward_decl(self, state: State, fdecl: ForwardDecl) -> None:
         self.block.forward_decls.append(fdecl)
 
diff --git a/cxxheaderparser/types.py b/cxxheaderparser/types.py
index f0bcc5e..79f6d45 100644
--- a/cxxheaderparser/types.py
+++ b/cxxheaderparser/types.py
@@ -38,6 +38,26 @@ class Value:
     tokens: typing.List[Token]
 
 
+@dataclass
+class NamespaceAlias:
+    """
+    A namespace alias
+
+    .. code-block:: c++
+
+        namespace ANS = my::ns;
+                  ~~~   ~~~~~~
+
+    """
+
+    alias: str
+
+    #: These are the names (split by ::) for the namespace that this alias
+    #: refers to, but does not include any parent namespace names. It may
+    #: include a leading "::", but does not include a following :: string.
+    names: typing.List[str]
+
+
 @dataclass
 class NamespaceDecl:
     """
diff --git a/cxxheaderparser/visitor.py b/cxxheaderparser/visitor.py
index c6d0d81..6f5708c 100644
--- a/cxxheaderparser/visitor.py
+++ b/cxxheaderparser/visitor.py
@@ -14,6 +14,7 @@ from .types import (
     FriendDecl,
     Function,
     Method,
+    NamespaceAlias,
     TemplateInst,
     Typedef,
     UsingAlias,
@@ -94,6 +95,11 @@ class CxxVisitor(Protocol):
         Called at the end of a ``namespace`` block
         """
 
+    def on_namespace_alias(self, state: State, alias: NamespaceAlias) -> None:
+        """
+        Called when a ``namespace`` alias is encountered
+        """
+
     def on_forward_decl(self, state: State, fdecl: ForwardDecl) -> None:
         """
         Called when a forward declaration is encountered
diff --git a/tests/test_namespaces.py b/tests/test_namespaces.py
index 7535889..0b6892f 100644
--- a/tests/test_namespaces.py
+++ b/tests/test_namespaces.py
@@ -4,6 +4,7 @@ from cxxheaderparser.errors import CxxParseError
 from cxxheaderparser.types import (
     ForwardDecl,
     FundamentalSpecifier,
+    NamespaceAlias,
     NameSpecifier,
     PQName,
     Token,
@@ -168,3 +169,29 @@ def test_invalid_inline_namespace() -> None:
     err = "<str>:1: parse error evaluating 'inline': a nested namespace definition cannot be inline"
     with pytest.raises(CxxParseError, match=re.escape(err)):
         parse_string(content, cleandoc=True)
+
+
+def test_ns_alias() -> None:
+    content = """
+      namespace ANS = my::ns;
+    """
+    data = parse_string(content, cleandoc=True)
+
+    assert data == ParsedData(
+        namespace=NamespaceScope(
+            ns_alias=[NamespaceAlias(alias="ANS", names=["my", "ns"])]
+        )
+    )
+
+
+def test_ns_alias_global() -> None:
+    content = """
+      namespace ANS = ::my::ns;
+    """
+    data = parse_string(content, cleandoc=True)
+
+    assert data == ParsedData(
+        namespace=NamespaceScope(
+            ns_alias=[NamespaceAlias(alias="ANS", names=["::", "my", "ns"])]
+        )
+    )