diff --git a/lsp_client/__init__.py b/lsp_client/__init__.py
index eabe3fb..ca6af74 100644
--- a/lsp_client/__init__.py
+++ b/lsp_client/__init__.py
@@ -15,6 +15,7 @@
     InitializeParams,
     InitializeRequest,
     InitializedNotification,
+    LanguageKind,
     Message,
     NotificationMessage,
     Position,
@@ -68,6 +69,7 @@
     "InitializeRequest",
     "InitializedNotification",
     "LSPClient",
+    "LanguageKind",
     "Message",
     "NotificationMessage",
     "PositionEncodingKind",
diff --git a/lsp_client/protocol.py b/lsp_client/protocol.py
index 2246cf7..1a439d0 100644
--- a/lsp_client/protocol.py
+++ b/lsp_client/protocol.py
@@ -267,9 +267,85 @@ def __init__(self, **kwargs: Any) -> None:
 # See https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_synchronization # noqa: E501
 
 
+class LanguageKind(str, Enum):
+    """The recognised language identifiers for a :class:`TextDocumentItem`.
+
+    The LSP types ``languageId`` simply as ``string`` and documents the set of
+    identifiers below. These are provided for convenience; custom identifiers
+    not listed here remain valid (``languageId`` accepts any string).
+
+    See
+    https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocumentItem
+    """
+
+    ABAP = "abap"
+    WindowsBat = "bat"
+    BibTeX = "bibtex"
+    Clojure = "clojure"
+    Coffeescript = "coffeescript"
+    C = "c"
+    CPP = "cpp"
+    CSharp = "csharp"
+    CSS = "css"
+    Diff = "diff"
+    Dart = "dart"
+    Dockerfile = "dockerfile"
+    Elixir = "elixir"
+    Erlang = "erlang"
+    FSharp = "fsharp"
+    GitCommit = "git-commit"
+    GitRebase = "git-rebase"
+    Go = "go"
+    Groovy = "groovy"
+    Handlebars = "handlebars"
+    HTML = "html"
+    Ini = "ini"
+    Java = "java"
+    JavaScript = "javascript"
+    JavaScriptReact = "javascriptreact"
+    JSON = "json"
+    LaTeX = "latex"
+    Less = "less"
+    Lua = "lua"
+    Makefile = "makefile"
+    Markdown = "markdown"
+    ObjectiveC = "objective-c"
+    ObjectiveCPP = "objective-cpp"
+    Perl = "perl"
+    Perl6 = "perl6"
+    PHP = "php"
+    Powershell = "powershell"
+    Pug = "jade"
+    Python = "python"
+    R = "r"
+    Razor = "razor"
+    Ruby = "ruby"
+    Rust = "rust"
+    SCSS = "scss"
+    Sass = "sass"
+    Scala = "scala"
+    ShaderLab = "shaderlab"
+    ShellScript = "shellscript"
+    SQL = "sql"
+    Swift = "swift"
+    TypeScript = "typescript"
+    TypeScriptReact = "typescriptreact"
+    TeX = "tex"
+    VisualBasic = "vb"
+    XML = "xml"
+    XSL = "xsl"
+    YAML = "yaml"
+
+
 class TextDocumentItem(BaseModel):
+    """An item to transfer a text document from the client to the server.
+
+    ``languageId`` is a free-form string per the spec; :class:`LanguageKind`
+    enumerates the documented identifiers for convenience.
+    """
+
     uri: str
-    languageId: str
+    languageId: LanguageKind | str
     version: int
     text: str
 
diff --git a/tests/test_protocol.py b/tests/test_protocol.py
index 56a2772..9e7944c 100644
--- a/tests/test_protocol.py
+++ b/tests/test_protocol.py
@@ -17,6 +17,7 @@
     InitializeParams,
     InitializeRequest,
     InitializedNotification,
+    LanguageKind,
     Message,
     NotificationMessage,
     Position,
@@ -32,6 +33,7 @@
     TextDocumentDidCloseNotification,
     TextDocumentDidOpenNotification,
     TextDocumentIdentifier,
+    TextDocumentItem,
     TextDocumentPositionParams,
     WorkDoneProgressBegin,
     WorkDoneProgressCancelNotification,
@@ -264,6 +266,56 @@ def test_response_message_null_id():
     assert data["id"] is None
 
 
+def test_language_kind_values():
+    assert LanguageKind.Python == "python"
+    assert LanguageKind.CPP == "cpp"
+    assert LanguageKind.GitCommit == "git-commit"
+    assert LanguageKind.TypeScriptReact == "typescriptreact"
+
+
+def test_text_document_item_with_language_kind():
+    item = TextDocumentItem(
+        uri="file:///tmp/test.py",
+        languageId=LanguageKind.Python,
+        version=1,
+        text="print(1)",
+    )
+    data = item.model_dump()
+    assert data == {
+        "uri": "file:///tmp/test.py",
+        "languageId": "python",
+        "version": 1,
+        "text": "print(1)",
+    }
+
+
+def test_text_document_item_with_known_string():
+    item = TextDocumentItem(
+        uri="file:///tmp/a.rs", languageId="rust", version=2, text="fn main(){}"
+    )
+    assert item.model_dump()["languageId"] == "rust"
+
+
+def test_text_document_item_allows_custom_language_id():
+    # languageId is a free-form string; unlisted identifiers stay valid.
+    item = TextDocumentItem(
+        uri="file:///tmp/a.cob", languageId="cobol", version=1, text=""
+    )
+    assert item.model_dump()["languageId"] == "cobol"
+
+
+def test_text_document_item_serialises_over_the_wire():
+    import json
+
+    item = TextDocumentItem(
+        uri="file:///tmp/test.py",
+        languageId=LanguageKind.Python,
+        version=1,
+        text="x = 1",
+    )
+    assert json.loads(json.dumps(item.model_dump()))["languageId"] == "python"
+
+
 def test_position_serialises():
     pos = Position(line=3, character=10)
     assert pos.model_dump() == {"line": 3, "character": 10}