diff --git a/src/darkleaf/di/core.clj b/src/darkleaf/di/core.clj
index 0e41eb05..2e6d6687 100644
--- a/src/darkleaf/di/core.clj
+++ b/src/darkleaf/di/core.clj
@@ -22,7 +22,8 @@
    (clojure.lang IDeref IFn Var Indexed ILookup)
    (java.io FileNotFoundException Writer)
    (java.lang AutoCloseable)
-   (java.util.function Function)))
+   (java.util.function Function)
+   (java.util.concurrent ConcurrentHashMap)))
 
 (set! *warn-on-reflection* true)
 
@@ -959,3 +960,56 @@
                                   (implicit-root key)
                                   with-inspect])]
     @components))
+
+
+(defn- first-mw? [registry]
+  (identical? registry initial-registry))
+
+(defn- add-factory-watch [factory f]
+  (when-some [var (-> factory p/description ::variable)]
+    ;; Every memoize instance has a new factory instance for a var.
+    ;; It is ok to pass a factory as a key.
+    (add-watch var factory (fn [_ _ _ _] (f)))))
+
+(defn- remove-factory-watch [factory]
+  (when-some [var (-> factory p/description ::variable)]
+    (remove-watch var factory)))
+
+(defn ->memoize
+  "Returns a statefull middleware that memoizes all registry build accesses.
+
+  To stop all memoized components use `(di/stop mem)`."
+  ^AutoCloseable [& middlewares]
+  (let [registry  (apply-middlewares initial-registry middlewares)
+        factories (ConcurrentHashMap.)
+        objs      (ConcurrentHashMap.)
+        ctx       {:*stop-list (atom '())}
+        add-stop  (->add-stop ctx)]
+    (reify
+      AutoCloseable
+      (close [this]
+        (doseq [[_ factory] factories]
+          (remove-factory-watch factory))
+        (.clear factories)
+        (.clear objs)
+        (try-stop-started ctx))
+      Function
+      (apply [this previous-registry]
+        (when-not (first-mw? previous-registry)
+          (throw (ex-info "A memoized registry should be the first middleware"
+                          {:type ::wrong-memoized-registry-position})))
+        (fn [key]
+          (let [factory (.computeIfAbsent factories key
+                                          (fn [_]
+                                            (let [factory (registry key)]
+                                              (add-factory-watch factory
+                                                                 #(.remove factories key factory))
+                                              factory)))]
+            (reify p/Factory
+              (dependencies [_]
+                (p/dependencies factory))
+              (build [_ deps _add-stop]
+                (.computeIfAbsent objs [factory deps]
+                                  (fn [_] (p/build factory deps add-stop))))
+              (description [_]
+                (p/description factory)))))))))
diff --git a/test/darkleaf/di/memoize_test.clj b/test/darkleaf/di/memoize_test.clj
new file mode 100644
index 00000000..70f4593e
--- /dev/null
+++ b/test/darkleaf/di/memoize_test.clj
@@ -0,0 +1,261 @@
+(ns darkleaf.di.memoize-test
+  (:require
+   [clojure.test :as t]
+   [darkleaf.di.core :as di]
+   [darkleaf.di.utils :refer [catch-some]]))
+
+(set! *warn-on-reflection* true)
+
+(t/deftest memoize-test
+  (let [a         'a
+        identity* (memoize identity)]
+    (identity* a)
+    (t/is (not (identical? a  (identity  'a))))
+    (t/is      (identical? a  (identity* 'a)))))
+
+(defn- some+identical? [a b]
+  (and (some? a)
+       (some? b)
+       (identical? a b)))
+
+(defn- some+not-identical? [a b]
+  (and (some? a)
+       (some? b)
+       (not (identical? a b))))
+
+
+(defn a
+  {::di/kind :component}
+  [{_ ::param}]
+  (Object.))
+
+
+(t/deftest changed-not-identical-test
+  (with-open [mem    (di/->memoize    {::param (Object.)})
+              first  (di/start `a mem)
+              second (di/start `a mem {::param (Object.)})]
+    (t/is (some+not-identical? @first @second))))
+
+
+(t/deftest changed-equal-and-identical-test
+  (with-open [mem    (di/->memoize    {::param :equal-and-identical})
+              first  (di/start `a mem)
+              second (di/start `a mem {::param :equal-and-identical})]
+    (t/is (some+identical? @first @second))))
+
+
+(t/deftest changed-equal-but-not-identical-test
+  (with-open [mem    (di/->memoize    {::param 'equal-but-not-identical})
+              first  (di/start `a mem)
+              second (di/start `a mem {::param 'equal-but-not-identical})]
+    (t/is (some+identical? @first @second))))
+
+
+(t/deftest changed-equal-but-different-test
+  (with-open [mem    (di/->memoize    {::param []})
+              first  (di/start `a mem)
+              second (di/start `a mem {::param '()})]
+    (t/is (some+identical? @first @second))))
+
+(t/deftest start-stop-order-test
+  (let [log    (atom [])
+        log-mw (fn [key-predicate]
+                 (di/log :after-build!
+                         #(when (key-predicate (:key %))
+                            (swap! log conj [:start (:key %)]))
+                         :after-demolish!
+                         #(when (key-predicate (:key %))
+                            (swap! log conj [:stop  (:key %)]))))
+        mem    (di/->memoize {::param :param} (log-mw any?))]
+    (-> (di/start `a mem)
+        (di/stop))
+    (t/is (= [[:start ::param]
+              [:start `a]]
+             @log))
+    (swap! log empty)
+
+    (-> (di/start `a mem)
+        (di/stop))
+    (t/is (= [] @log))
+
+    (-> (di/start `a mem
+                  {::param :new-param}
+                  (log-mw #{::param}))
+        (di/stop))
+    (t/is (= [[:start ::param]
+              [:start `a]
+              [:stop ::param]]
+             @log))
+    (swap! log empty)
+
+    (di/stop mem)
+    (t/is (= [[:stop `a]
+              [:stop `a]
+              [:stop ::param]]
+             @log))
+    (swap! log empty)
+
+    (-> (di/start `a mem)
+        (di/stop))
+    (t/is (= [[:start ::param]
+              [:start `a]]
+             @log))))
+
+(t/deftest should-be-first-test
+  (with-open [mem (di/->memoize)]
+    (let [ex (catch-some (di/start `a {::param 42} mem))]
+      (t/is (= ::di/wrong-memoized-registry-position
+               (-> ex ex-data :type))))))
+
+
+(t/deftest service-deps+body-change-test
+  (with-open [mem (di/->memoize {::param-1 42
+                                 ::param-2 0})]
+
+    (defn service-1 [{param ::param-1}]
+      [:a param])
+    (with-open [s (di/start `service-1 mem)]
+      (t/is (= [:a 42] (s))))
+
+    (defn service-1 [{param ::param-2}]
+      [:b param])
+    (with-open [s (di/start `service-1 mem)]
+      (t/is (= [:b 0] (s))))))
+
+
+(t/deftest component-deps+body-change-test
+  (with-open [mem (di/->memoize {::param-1 42
+                                 ::param-2 0})]
+
+    (defn component-1
+      {::di/kind :component}
+      [{param ::param-1}]
+      [:a param])
+    (with-open [s (di/start `component-1 mem)]
+      (t/is (= [:a 42] @s)))
+
+    (defn component-1
+      {::di/kind :component}
+      [{param ::param-2}]
+      [:b param])
+    (with-open [s (di/start `component-1 mem)]
+      (t/is (= [:b 0] @s)))))
+
+
+(t/deftest var-type-change-test
+  (with-open [mem (di/->memoize {::param 42})]
+
+    (def var-type-change-var :just-value)
+    (with-open [s (di/start `var-type-change-var mem)]
+      (t/is (= :just-value @s)))
+
+    (defn var-type-change-var
+      {::di/kind :component}
+      [{param ::param}]
+      [:a param])
+    (with-open [s (di/start `var-type-change-var mem)]
+      (t/is (= [:a 42] @s)))))
+
+
+(t/deftest remove-watch-test
+  (def remove-watch-var :_)
+  (with-open [mem (di/->memoize)
+              s   (di/start `remove-watch-var mem)])
+  (t/is (= {} (.getWatches #'remove-watch-var))))
+
+
+
+(t/deftest invalidation-log-test
+  (let [log    (atom [])
+        log-mw (di/log :after-build!
+                       #(swap! log conj [:start (:key %)])
+                       :after-demolish!
+                       #(swap! log conj [:stop  (:key %)]))
+        mem    (di/->memoize {::param :param} log-mw)]
+
+    (defn invalidation-a []
+      :a)
+
+    (defn invalidation-b [{a `invalidation-a}]
+      (a))
+
+    (-> (di/start `invalidation-b mem)
+        (di/stop))
+    (t/is (= [[:start `invalidation-a]
+              [:start `invalidation-b]]
+             @log))
+    (swap! log empty)
+
+    (-> (di/start `invalidation-b mem)
+        (di/stop))
+    (t/is (= [] @log))
+
+
+    (defn invalidation-a []
+      :a')
+
+    ;; A service without arguments is just a var
+    ;; so `invalidation-b` received the same arguments.
+    (-> (di/start `invalidation-b mem)
+        (di/stop))
+    (t/is (= [[:start `invalidation-a]]
+             @log))
+    (swap! log empty)
+
+
+    (defn invalidation-a [{param ::param}]
+      :a'')
+
+    (-> (di/start `invalidation-b mem)
+        (di/stop))
+    (t/is (= [[:start ::param]
+              [:start `invalidation-a]
+              [:start `invalidation-b]]
+             @log))
+    (swap! log empty)
+
+
+    (di/stop mem)
+    (t/is (= [[:stop `invalidation-b]
+              [:stop `invalidation-a]
+              [:stop ::param]
+              [:stop `invalidation-a]
+              [:stop `invalidation-b]
+              [:stop `invalidation-a]]
+             @log))))
+
+(comment
+
+  (require '[clj-async-profiler.core :as prof])
+  (prof/serve-ui 8080)
+
+
+  (def N 10000)
+
+  (prof/profile {}
+    (dotimes [_ N]
+      (di/start `a {::param 42})))
+
+
+
+  (let [mem (di/->memoize {::param 42})]
+    (prof/profile {}
+      (dotimes [_ N]
+        (di/start `a mem))))
+
+
+  (prof/generate-diffgraph 1 2 {})
+
+
+
+  (time
+    (dotimes [_ N]
+      (di/start `a {::param 42})))
+
+  (let [mem (di/->memoize {::param 42})]
+    (time
+      (dotimes [_ N]
+        (di/start `a mem))))
+
+
+ ,,,)