diff --git a/lib/brrer/brrer.ml b/lib/brrer/brrer.ml
index ffec73c..ac069b4 100644
--- a/lib/brrer/brrer.ml
+++ b/lib/brrer/brrer.ml
@@ -69,3 +69,5 @@ module Brr_canvas = Brr_canvas
 module Fut = Fut
 module Intersection_observer = Intersection_observer
 module Mutation_observer = Mutation_observer
+module Resize_observer = Resize_observer
+module Dom_rect_read_only = Dom_rect_read_only
diff --git a/lib/brrer/dom_rect_read_only.ml b/lib/brrer/dom_rect_read_only.ml
new file mode 100644
index 0000000..792be94
--- /dev/null
+++ b/lib/brrer/dom_rect_read_only.ml
@@ -0,0 +1,12 @@
+type t = Jv.t
+
+external of_jv : Jv.t -> t = "%identity"
+
+let x t = Jv.get t "x" |> Jv.to_int
+let y t = Jv.get t "y" |> Jv.to_int
+let width t = Jv.get t "width" |> Jv.to_int
+let height t = Jv.get t "height" |> Jv.to_int
+let top t = Jv.get t "top" |> Jv.to_int
+let right t = Jv.get t "right" |> Jv.to_int
+let bottom t = Jv.get t "bottom" |> Jv.to_int
+let left t = Jv.get t "left" |> Jv.to_int
diff --git a/lib/brrer/dom_rect_read_only.mli b/lib/brrer/dom_rect_read_only.mli
new file mode 100644
index 0000000..8264cbe
--- /dev/null
+++ b/lib/brrer/dom_rect_read_only.mli
@@ -0,0 +1,15 @@
+(** Bindings to DOMRectReadOnly
+
+    https://developer.mozilla.org/en-US/docs/Web/API/DOMRectReadOnly *)
+
+type t
+
+val of_jv : Jv.t -> t
+val x : t -> int
+val y : t -> int
+val width : t -> int
+val height : t -> int
+val top : t -> int
+val right : t -> int
+val bottom : t -> int
+val left : t -> int
diff --git a/lib/brrer/resize_observer.ml b/lib/brrer/resize_observer.ml
new file mode 100644
index 0000000..357302b
--- /dev/null
+++ b/lib/brrer/resize_observer.ml
@@ -0,0 +1,63 @@
+open Brr
+
+type t = Jv.t
+
+external of_jv : Jv.t -> t = "%identity"
+
+module Entry = struct
+  type t = Jv.t
+
+  external of_jv : Jv.t -> t = "%identity"
+
+  type box_size = { block_size : int; inline_size : int }
+
+  let box_size_of_jv jv =
+    {
+      block_size = Jv.get jv "blockSize" |> Jv.to_int;
+      inline_size = Jv.get jv "inlineSize" |> Jv.to_int;
+    }
+
+  let border_box_size t = Jv.get t "borderBoxSize" |> Jv.to_array box_size_of_jv
+
+  let content_box_size t =
+    Jv.get t "contentBoxSize" |> Jv.to_array box_size_of_jv
+
+  let content_rect t = Jv.get t "contentRect" |> Dom_rect_read_only.of_jv
+
+  let device_pixel_content_box_size t =
+    Jv.get t "devicePixelContentBoxSize" |> Jv.to_array box_size_of_jv
+
+  let target t = Jv.get t "target" |> El.of_jv
+end
+
+type box = Content_box | Border_box | Device_pixel_content_box
+
+let string_of_box = function
+  | Content_box -> "content-box"
+  | Border_box -> "border-box"
+  | Device_pixel_content_box -> "device-pixel-content-box"
+
+let disconnect t = ignore @@ Jv.call t "disconnect" [||]
+
+let observe t ?box target =
+  let args =
+    let target = El.to_jv target in
+    match box with
+    | None -> [| target |]
+    | Some b ->
+        let box = Jv.obj [| ("box", Jv.of_string (string_of_box b)) |] in
+        [| target; box |]
+  in
+  Jv.call t "observe" args |> ignore
+
+let unobserve t target =
+  let target = El.to_jv target in
+  ignore @@ Jv.call t "disconnect" [| target |]
+
+let create ~callback =
+  let callback entries observer =
+    let entries = Jv.to_list Entry.of_jv entries in
+    callback entries (of_jv observer)
+  in
+  let args = [| Jv.repr callback |] in
+  Jv.new' (Jv.get Jv.global "ResizeObserver") args
diff --git a/lib/brrer/resize_observer.mli b/lib/brrer/resize_observer.mli
new file mode 100644
index 0000000..c62b050
--- /dev/null
+++ b/lib/brrer/resize_observer.mli
@@ -0,0 +1,29 @@
+(** Bindings to the ResizeObserver API
+    @see https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver
+*)
+
+type t
+
+val of_jv : Jv.t -> t
+
+module Entry : sig
+  type t
+
+  val of_jv : Jv.t -> t
+
+  type box_size = { block_size : int; inline_size : int }
+
+  val box_size_of_jv : t -> box_size
+  val border_box_size : t -> box_size array
+  val content_box_size : t -> box_size array
+  val content_rect : t -> Dom_rect_read_only.t
+  val device_pixel_content_box_size : t -> box_size array
+  val target : t -> Brr.El.t
+end
+
+type box = Content_box | Border_box | Device_pixel_content_box
+
+val disconnect : t -> unit
+val observe : t -> ?box:box -> Brr.El.t -> unit
+val unobserve : t -> Brr.El.t -> unit
+val create : callback:(Entry.t list -> t -> unit) -> t