diff --git a/src/gen_rules.ml b/src/gen_rules.ml
index 782cdbff..21d9f7a4 100644
--- a/src/gen_rules.ml
+++ b/src/gen_rules.ml
@@ -1410,7 +1410,7 @@ module Gen(P : Params) = struct
       | Ocamllex     conf -> ocamllex_rules    conf ~dir
       | Ocamlyacc    conf -> ocamlyacc_rules   conf ~dir
       | Alias        alias -> alias_rules alias ~dir
-      | Provides _ | Install _ | Other -> ())
+      | Provides _ | Install _ -> ())
 
   let () = List.iter P.stanzas ~f:rules
 
diff --git a/src/jbuild_load.ml b/src/jbuild_load.ml
index d7dd689b..88eea83e 100644
--- a/src/jbuild_load.ml
+++ b/src/jbuild_load.ml
@@ -8,10 +8,27 @@ type conf =
   ; packages  : Path.t String_map.t
   }
 
-let load ~dir ~visible_packages =
-  let stanzas = Sexp_load.many (Path.relative dir "jbuild" |> Path.to_string) Stanza.vjs in
+let load ~dir ~visible_packages ~version =
+  let version, stanzas =
+    Sexp_load.many (Path.relative dir "jbuild" |> Path.to_string)
+      (fun sexps ->
+         let versions, stanzas =
+           List.partition_map sexps ~f:(function
+             | List [Atom ("jbuilder_version" | "Jbuilder_version"); ver] as sexp ->
+               Inl (Jbuilder_version.t ver, sexp)
+             | sexp -> Inr sexp)
+         in
+         let version =
+           match versions with
+           | [] -> version
+           | [(v, _)] -> v
+           | _ :: (_, sexp) :: _ ->
+             of_sexp_error "jbuilder_version specified too many times" sexp
+         in
+         (version, List.filter_map sexps ~f:(Stanza.select version)))
+  in
   let stanzas = Stanza.resolve_packages stanzas ~dir ~visible_packages in
-  (dir, stanzas)
+  (version, stanzas)
 
 let load () =
   let ftree = File_tree.load Path.root in
@@ -38,7 +55,7 @@ let load () =
     |> List.map ~f:(fun (pkg, path) -> (path, pkg))
     |> Path.Map.of_alist_multi
   in
-  let rec walk dir stanzas visible_packages =
+  let rec walk dir stanzas visible_packages version =
     let path = File_tree.Dir.path dir in
     let files = File_tree.Dir.files dir in
     let sub_dirs = File_tree.Dir.sub_dirs dir in
@@ -49,6 +66,13 @@ let load () =
         List.fold_left pkgs ~init:visible_packages ~f:(fun acc pkg ->
           String_map.add acc ~key:pkg ~data:path)
     in
+    let version, stanzas =
+      if String_set.mem "jbuild" files then
+        let version, stanzas_here = load ~dir:path ~visible_packages ~version in
+        (version, (path, stanzas_here) :: stanzas)
+      else
+        (version, stanzas)
+    in
     let sub_dirs =
       if String_set.mem "jbuild-ignore" files then
         let ignore_set =
@@ -63,20 +87,13 @@ let load () =
     let children, stanzas =
       String_map.fold sub_dirs ~init:([], stanzas)
         ~f:(fun ~key:_ ~data:dir (children, stanzas) ->
-          let child, stanzas = walk dir stanzas visible_packages in
+          let child, stanzas = walk dir stanzas visible_packages version in
           (child :: children, stanzas))
     in
-    let stanzas =
-      if String_set.mem "jbuild" files then
-        load ~dir:path ~visible_packages
-        :: stanzas
-      else
-        stanzas
-    in
     (Alias.Node (path, children), stanzas)
   in
   let root = File_tree.root ftree in
-  let tree, stanzas = walk root [] String_map.empty in
+  let tree, stanzas = walk root [] String_map.empty Jbuilder_version.latest_stable in
   { file_tree = ftree
   ; tree
   ; stanzas
diff --git a/src/jbuild_types.ml b/src/jbuild_types.ml
index 2b323cdb..5c4f8efa 100644
--- a/src/jbuild_types.ml
+++ b/src/jbuild_types.ml
@@ -11,6 +11,20 @@ open Sexp.Of_sexp
 type sexp = Sexp.t = Atom of string | List of sexp list
 let of_sexp_error = Sexp.of_sexp_error
 
+module Jbuilder_version = struct
+  type t =
+    | V1
+    | Vjs
+
+  let t =
+    enum
+      [ "1", V1
+      ; "jane_street", Vjs
+      ]
+
+  let latest_stable = V1
+end
+
 let invalid_module_name sexp =
   of_sexp_error "invalid module name" sexp
 
@@ -749,36 +763,47 @@ module Stanza = struct
     | Provides    of Provides.t
     | Install     of Install_conf.t
     | Alias       of Alias_conf.t
-    | Other
+
+  let cstr' name args f =
+    cstr name args (fun x -> Some (f x))
 
   let v1 =
     sum
-      [ cstr "library"     [Library.v1]      (fun x -> Library     x)
-      ; cstr "executables" [Executables.v1]  (fun x -> Executables x)
-      ; cstr "rule"        [Rule.v1]         (fun x -> Rule        x)
-      ; cstr "ocamllex"    [Ocamllex.v1]     (fun x -> Ocamllex    x)
-      ; cstr "ocamlyacc"   [Ocamlyacc.v1]    (fun x -> Ocamlyacc   x)
-      ; cstr "provides"    [Provides.v1]     (fun x -> Provides    x)
-      ; cstr "install"     [Install_conf.v1] (fun x -> Install     x)
-      ; cstr "alias"       [Alias_conf.v1]   (fun x -> Alias       x)
+      [ cstr' "library"     [Library.v1]      (fun x -> Library     x)
+      ; cstr' "executables" [Executables.v1]  (fun x -> Executables x)
+      ; cstr' "rule"        [Rule.v1]         (fun x -> Rule        x)
+      ; cstr' "ocamllex"    [Ocamllex.v1]     (fun x -> Ocamllex    x)
+      ; cstr' "ocamlyacc"   [Ocamlyacc.v1]    (fun x -> Ocamlyacc   x)
+      ; cstr' "provides"    [Provides.v1]     (fun x -> Provides    x)
+      ; cstr' "install"     [Install_conf.v1] (fun x -> Install     x)
+      ; cstr' "alias"       [Alias_conf.v1]   (fun x -> Alias       x)
+      (* Just for validation and error messages *)
+      ; cstr "jbuilder_version" [Jbuilder_version.t] (fun _ -> None)
       ]
 
   let vjs =
+    let ign name = cstr name [fun _ -> ()] (fun () -> None) in
     sum
-      [ cstr "library"     [Library.vjs]      (fun x -> Library     x)
-      ; cstr "executables" [Executables.vjs]  (fun x -> Executables x)
-      ; cstr "rule"        [Rule.vjs]         (fun x -> Rule        x)
-      ; cstr "ocamllex"    [Ocamllex.vjs]     (fun x -> Ocamllex    x)
-      ; cstr "ocamlyacc"   [Ocamlyacc.vjs]    (fun x -> Ocamlyacc   x)
-      ; cstr "provides"    [Provides.vjs]     (fun x -> Provides    x)
-      ; cstr "install"     [Install_conf.vjs] (fun x -> Install     x)
-      ; cstr "alias"       [Alias_conf.vjs]   (fun x -> Alias       x)
-      ; cstr "enforce_style"         [fun _ -> ()] (fun _ -> Other )
-      ; cstr "toplevel_expect_tests" [fun _ -> ()] (fun _ -> Other)
-      ; cstr "unified_tests"         [fun _ -> ()] (fun _ -> Other)
-      ; cstr "embed"                 [fun _ -> ()] (fun _ -> Other)
+      [ cstr' "library"     [Library.vjs]      (fun x -> Library     x)
+      ; cstr' "executables" [Executables.vjs]  (fun x -> Executables x)
+      ; cstr' "rule"        [Rule.vjs]         (fun x -> Rule        x)
+      ; cstr' "ocamllex"    [Ocamllex.vjs]     (fun x -> Ocamllex    x)
+      ; cstr' "ocamlyacc"   [Ocamlyacc.vjs]    (fun x -> Ocamlyacc   x)
+      ; cstr' "provides"    [Provides.vjs]     (fun x -> Provides    x)
+      ; cstr' "install"     [Install_conf.vjs] (fun x -> Install     x)
+      ; cstr' "alias"       [Alias_conf.vjs]   (fun x -> Alias       x)
+      ; ign "enforce_style"
+      ; ign "toplevel_expect_tests"
+      ; ign "unified_tests"
+      ; ign "embed"
+      (* Just for validation and error messages  *)
+      ; cstr "jbuilder_version" [Jbuilder_version.t] (fun _ -> None)
       ]
 
+  let select : Jbuilder_version.t -> Sexp.t -> t option = function
+    | V1  -> v1
+    | Vjs -> vjs
+
   let lib_names ts =
     List.fold_left ts ~init:String_set.empty ~f:(fun acc (_, stanzas) ->
       List.fold_left stanzas ~init:acc ~f:(fun acc -> function
diff --git a/src/sexp.ml b/src/sexp.ml
index a38d2541..f56c19db 100644
--- a/src/sexp.ml
+++ b/src/sexp.ml
@@ -328,6 +328,24 @@ module Of_sexp = struct
       | Atom s ->
         let (Constructor_spec.T c) = find_cstr cstrs sexp s in
         Constructor_args_spec.convert c.args sexp args c.make
+
+  let enum cstrs sexp =
+    match sexp with
+    | List _ -> of_sexp_error "Atom expected" sexp
+    | Atom s ->
+      match
+        List.find cstrs ~f:(fun (name, _) ->
+          equal_cstr_name name s)
+      with
+      | Some (_, value) -> value
+      | None ->
+        of_sexp_error
+          (sprintf "Unknown value %s%s" s
+             (hint
+                (String.uncapitalize_ascii s)
+                (List.map cstrs ~f:(fun (name, _) ->
+                   String.uncapitalize_ascii name)))
+          ) sexp
 end
 (*
 module Both = struct
diff --git a/src/sexp.mli b/src/sexp.mli
index 8ef2cdd6..e2882eb6 100644
--- a/src/sexp.mli
+++ b/src/sexp.mli
@@ -68,4 +68,6 @@ module Of_sexp : sig
   val sum
     :  'a Constructor_spec.t list
     -> 'a t
+
+  val enum : (string * 'a) list -> 'a t
 end
diff --git a/src/sexp_load.ml b/src/sexp_load.ml
index 69128860..e747ad32 100644
--- a/src/sexp_load.ml
+++ b/src/sexp_load.ml
@@ -20,7 +20,7 @@ let many fn f =
     |> List.split
   in
   try
-    List.map sexps ~f
+    f sexps
   with Sexp.Of_sexp_error (msg, sub) ->
     let loc =
       match Sexp.locate_in_list sexps ~sub ~locs with
diff --git a/src/sexp_load.mli b/src/sexp_load.mli
index 5e0b87d9..05f134df 100644
--- a/src/sexp_load.mli
+++ b/src/sexp_load.mli
@@ -1,4 +1,4 @@
 open! Import
 
 val single : string -> (Sexp.t -> 'a) -> 'a
-val many   : string -> (Sexp.t -> 'a) -> 'a list
+val many   : string -> (Sexp.t list -> 'a) -> 'a