diff --git a/docs/index.rst b/docs/index.rst
index 3edb7748..a0b96729 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -12,6 +12,7 @@ Contents:
    :maxdepth: 2
 
    intro.rst
+   lang.rst
 
 Indices and tables
 ==================
diff --git a/docs/lang.rst b/docs/lang.rst
new file mode 100644
index 00000000..3532d347
--- /dev/null
+++ b/docs/lang.rst
@@ -0,0 +1,87 @@
+Language
+========
+
+The language provided by picrin.
+
+Libraries
+---------
+
+- `(scheme base)`
+- `(scheme write)`
+- `(scheme cxr)`
+- `(scheme file)`
+- `(scheme inexact)`
+- `(scheme time)`
+- `(scheme process-context)`
+- `(scheme load)`
+- `(scheme lazy)`
+- `(picrin macro)`
+
+  - `define-macro`
+  - `gensym`
+  - `macroexpand`
+
+  Old-fashioned macro.
+
+  - `make-syntactic-closure`
+  - `identifier?`
+  - `identifier=?`
+
+  Syntactic closures.
+
+  - `er-macro-transformer`
+  - `ir-macro-transformer`
+
+  Explicit renaming macro family.
+
+- `(picrin regexp)`
+
+  - `(regexp? obj)`
+  - `(regexp ptrn [flags])`
+
+  Compiles pattern string into a regexp object. A string `flags` may contain any of #\g, #\i, #\m.
+
+  - `(regexp-match re input)`
+
+  Returns two values: a list of match strings, and a list of match indeces.
+
+  - `(regexp-replace re input txt)`
+  - `(regexp-split re input)`
+
+- `(picrin control)`
+
+  - `(reset h)`
+  - `(shift k)`
+
+  Delimited control operators.
+
+- `(picrin user)`
+
+  When you start the REPL, you are dropped into here.
+
+- `(srfi 1)`
+
+  List manipulation library.
+
+- `(srfi 26)`
+
+  Cut/cute macros.
+
+- `(srfi 95)`
+
+  Sorting and Marging.
+
+The REPL
+--------
+
+At the REPL start-up time, some usuful built-in libraries listed below will be automatically imported.
+
+- `(scheme base)`
+- `(scheme load)`
+- `(scheme process-context)`
+- `(scheme write)`
+- `(scheme file)`
+- `(scheme inexact)`
+- `(scheme cxr)`
+- `(scheme lazy)`
+- `(scheme time)`