diff --git a/src/taoensso/encore/flow.cljc b/src/taoensso/encore/flow.cljc
new file mode 100644
index 00000000..a09aa632
--- /dev/null
+++ b/src/taoensso/encore/flow.cljc
@@ -0,0 +1,158 @@
+(ns taoensso.encore.flow
+  "Alpha, subject to change without notice!
+  Low-level toolkit for building context flows.
+  Used by Telemere, etc.
+
+  Flows provide:
+    - Namespaced dynamic state
+    - Wrapping init
+    - Wrapping or mutable namespaced updates
+    - Flow paths with delta timings"
+
+  {:added "vX.Y.Z (YYYY-MM-DD)"}
+  (:require
+   [clojure.string  :as str]
+   [taoensso.encore :as enc :refer [have have?]])
+
+  #?(:cljs
+     (:require-macros
+      [taoensso.encore.flow :as flow-macros :refer []])))
+
+(comment (remove-ns 'taoensso.encore.flow))
+
+;; Note: the common case for this API is to be wrapped by a consumer-level API.
+;; Expects `flows`: {<flow-id> <Flow_>} dynamic var.
+
+(do
+  (deftype   Flow       [flow-id ^long total-nsecs path state ^long nst])
+  (defrecord FlowInfo   [flow-id ^long total-nsecs path state])  ; Public
+  (defrecord PathEntry  [flow-id ^long nsecs-delta ^long count]) ; Public
+  (deftype   FlowResult [form-result flow-info]))
+
+(defn ^:no-doc ^Flow new-flow
+  "Private implementation detail."
+  [incl-path? flow-id init-state]
+  (Flow. flow-id 0
+    (when incl-path? [(PathEntry. :flow/start 0 1)])
+    init-state (enc/now-nano*)))
+
+(comment (new-flow true :fid1 {}))
+
+(def ^:private aborted-flow
+  (Flow. :flow/aborted -1 nil nil -1))
+
+(defn ^:no-doc ^Flow update-flow
+  "Private implementation detail."
+  [^Flow flow step-id update-spec]
+  (if (identical? flow aborted-flow)
+    flow ; Noop
+    (let [nst         (enc/now-nano*)
+          nsecs-delta (- nst (.-nst flow))
+          new-path
+          (when-let [old-path (.-path flow)]
+            (let [^PathEntry last-pe (peek old-path)]
+              (if (enc/identical-kw? step-id (.-flow-id last-pe))
+                (conj (pop old-path) (PathEntry. step-id (.-nsecs-delta last-pe) (inc (.-count last-pe))))
+                (conj      old-path  (PathEntry. step-id    nsecs-delta          1)))))
+
+          new-state
+          (let [old-state (.-state flow)]
+            (enc/cond
+              (nil? update-spec)              old-state
+              (fn?  update-spec) (update-spec old-state)
+              (map? update-spec)
+              (if old-state
+                (conj old-state update-spec)
+                (do             update-spec))
+
+              :else
+              (enc/unexpected-arg! update-spec
+                {:context `update-flow
+                 :expected '#{nil fn map}})))]
+
+      (Flow. (.-flow-id flow)
+        (+ (.-total-nsecs flow) nsecs-delta)
+        new-path new-state nst))))
+
+(comment (update-flow (new-flow true :fid1 {}) :fid2 #(assoc % :foo :bar)))
+
+(defn ^:no-doc flow-info
+  "Private implementation detail."
+  ([^Flow flow end-flow?]
+   (when-not (identical? flow aborted-flow)
+     (let [final-flow (if end-flow? (update-flow flow :flow/end nil) flow)]
+       (FlowInfo.
+         (.-flow-id           flow)
+         (.-total-nsecs final-flow)
+         (.-path        final-flow)
+         (.-state       final-flow)))))
+
+  ([flows] ; {<flow-id> <FlowInfo>}
+   (not-empty
+     (reduce-kv
+       (fn [m flow-id flow_]
+         (let [flow @flow_]
+           (if (identical? aborted-flow flow)
+             (dissoc m flow-id)
+             (assoc  m flow-id (flow-info flow false)))))
+       flows
+       flows))))
+
+#?(:clj
+   (defmacro with-flow
+     "Executes given form within newly-initialized flow and returns `FlowResult`."
+     [flows incl-path? [flow-id init-state] form]
+     `(let [flow-id#     ~flow-id
+            flow_#       (atom (new-flow ~incl-path? flow-id# ~init-state))
+            form-result# (binding [~flows (assoc ~flows flow-id# flow_#)] ~form)]
+        (FlowResult. form-result# (flow-info @flow_# true)))))
+
+(defn get-flow
+  "Returns `Flow` or nil."
+  [flows flow-id]
+  (when-let [flow_ (get flows flow-id)]
+    (let [flow @flow_]
+      (if (identical? flow aborted-flow)
+        nil
+        flow))))
+
+(defn ^:no-doc flow-id-pair
+  "Private implementation detail."
+  [id-spec] (if (vector? id-spec) id-spec [:_default id-spec]))
+
+(defn ^:no-doc -update-flow!
+  "Private implementation detail."
+  [flows parent-id child-id update-spec]
+  (when-let [flow_ (get flows parent-id)]
+    (swap! flow_ (fn [old] (update-flow old child-id update-spec)))))
+
+#?(:clj
+   (defmacro update-flow!
+     "Returns updated `Flow`, or nil if given `parent-id` flow isn't already established."
+     [flows id-spec update-spec]
+     (let [id-spec (if (enc/const-form? id-spec) (flow-id-pair id-spec) id-spec)]
+       (if (vector? id-spec)
+         (let [[parent-id child-id] id-spec]
+           `(when-let [flows# ~flows]
+              (-update-flow! flows# ~parent-id ~child-id  ~update-spec)))
+
+         `(when-let [flows# ~flows]
+            (let [[parent-id# child-id#] (flow-id-pair ~id-spec)]
+              (update-flow! flows# parent-id# child-id# ~update-spec)))))))
+
+(defn abort-flow!
+  "If the named flow exists, aborts it and returns true.
+  Otherwise returns false."
+  [flows flow-id]
+  (if-let [flow_ (get flows flow-id)]
+    (enc/reset!? flow_ aborted-flow)
+    false))
+
+(comment
+  (do
+    (def ^:dynamic *flows* "{<flow-id> <Flow_>}" nil)
+    (with-flow     *flows* true [:fid1 {}] (+ 3 2)))
+
+  (.-flow-info
+    (with-flow     *flows* true [:fid1 {}]
+      (abort-flow! *flows* :fid1))))
diff --git a/test/taoensso/encore_tests.cljc b/test/taoensso/encore_tests.cljc
index c7977130..c00dc5ad 100644
--- a/test/taoensso/encore_tests.cljc
+++ b/test/taoensso/encore_tests.cljc
@@ -7,7 +7,9 @@
    [clojure.string  :as str]
    [taoensso.encore :as enc]
    [taoensso.encore.runner :as runner]
-   [taoensso.encore.ctx-filter :as cf])
+   [taoensso.encore.ctx-filter :as cf]
+   [taoensso.encore.flow :as flow #?@(:cljs (:refer [Flow FlowResult]))])
+  #?(:clj (:import [taoensso.encore.flow Flow FlowResult]))
 
   #?(:cljs
      (:require-macros
@@ -773,6 +775,103 @@
          (is (->> (cf/filter? nil [["*" :info]] "ns1" nil) (enc/throws? :common "Invalid level")))
          (is (->> (cf/filter? nil [["*" :info]] nil   nil) (enc/throws? :common "Invalid level")))])])])
 
+;;;; Flow
+
+(def ^:dynamic *flows* "{<flow-id> <Flow_>}" nil)
+
+(defn- submaps? [maps submaps] (enc/reduce-zip (fn [acc m sub] (and acc (enc/submap? m sub))) true maps submaps))
+(defn- subflow? [flow subflow]
+  (and
+    (enc/submap? (dissoc flow :path) (dissoc subflow :path))
+    (submaps?    (get    flow :path) (get    subflow :path))))
+
+(deftest _flow
+  [(let [flow-result (flow/with-flow *flows* true [:fid1 {:a :A}] (+ 3 2))]
+     [(is (=        (.-form-result flow-result) 5))
+      (is (subflow? (.-flow-info   flow-result)
+            {:flow-id :fid1, :state {:a :A}
+             :path
+             [{:flow-id :flow/start, :nsecs-delta :submap/ex, :count 1}
+              {:flow-id :flow/end,   :nsecs-delta :submap/ex, :count 1}]}))])
+
+   (let [flow-result
+         (flow/with-flow *flows* true [:fid1 {:a :A}]
+           (do
+             (flow/update-flow! *flows* :fid2 {:b :B}) ; = [:_default :fid2]
+             (flow/update-flow! *flows* [:__nx :fid3] {:c :C})
+             (flow/update-flow! *flows* [:fid1 :fid4] {:d :D})
+             (flow/update-flow! *flows* [:fid1 :fid5] #(assoc % :e :E))))]
+
+     [(is (subflow? (.-flow-info flow-result)
+            {:flow-id :fid1
+             :state {:a :A :d :D :e :E}
+             :path
+             [{:flow-id :flow/start, :nsecs-delta :submap/ex, :count 1}
+              {:flow-id :fid4,       :nsecs-delta :submap/ex, :count 1}
+              {:flow-id :fid5,       :nsecs-delta :submap/ex, :count 1}
+              {:flow-id :flow/end,   :nsecs-delta :submap/ex, :count 1}]})
+        "Updates are conditional on parent id, map update-specs can be maps or fns.")])
+
+   (let [flow-result
+         (flow/with-flow *flows* true [:fid1 {:a :A}]
+           (dotimes [_ 100] (flow/update-flow! *flows* [:fid1 :fid2] nil)))]
+
+     [(is (subflow? (.-flow-info flow-result)
+            {:path
+             [{:flow-id :flow/start, :nsecs-delta :submap/ex, :count 1}
+              {:flow-id :fid2,       :nsecs-delta :submap/ex, :count 100}
+              {:flow-id :flow/end,   :nsecs-delta :submap/ex, :count 1}]})
+        "Recursion increases path entry count")])
+
+   (testing "Aborted flows"
+     (let [flow-result
+           (flow/with-flow *flows* true [:fid1 {:a :A}]
+             [(flow/abort-flow!  *flows* :fid1)
+              (flow/abort-flow!  *flows* :fid1)
+              (flow/update-flow! *flows* [:fid1 :fid2] {:b :B})])]
+
+       [(let [[fr1 fr2 fr3] (.-form-result flow-result)]
+          [(is (= [fr1 fr2] [true false]))
+           (is (= (flow/flow-info fr3 true)           nil))
+           (is (= (flow/flow-info {:fid1 (atom fr3)}) nil))])]))
+
+   (testing "Nested flows"
+     (let [flow-result
+           (flow/with-flow *flows* true [:fid-a1 {:a1 :A1}]
+             (flow/with-flow *flows* true [:fid-b1 {:b1 :B1}]
+               (do
+                 (flow/update-flow! *flows* [:fid-a1 :fid-a2] {:a2 :A2})
+                 (flow/update-flow! *flows* [:fid-b1 :fid-b2] {:b2 :B2})
+                 (flow/flow-info    *flows*))))
+
+           {:keys [fid-a1 fid-b1] :as _inner-flow-info}
+           (.-form-result ^FlowResult
+             (.-form-result flow-result))]
+
+       [(is (subflow? fid-a1
+              {:flow-id :fid-a1,
+               :state {:a1 :A1, :a2 :A2},
+               :total-nsecs :submap/ex,
+               :path ; Note no :flow/end
+               [{:flow-id :flow/start, :nsecs-delta :submap/ex, :count 1}
+                {:flow-id :fid-a2,     :nsecs-delta :submap/ex, :count 1}]}))
+
+        (is (subflow? fid-b1
+              {:flow-id :fid-b1,
+               :state {:b1 :B1, :b2 :B2},
+               :total-nsecs :submap/ex,
+               :path ; Note no :flow/end
+               [{:flow-id :flow/start, :nsecs-delta :submap/ex, :count 1}
+                {:flow-id :fid-b2,     :nsecs-delta :submap/ex, :count 1}]}))
+
+        (is (subflow? (.flow-info flow-result) ; Outer flow-result
+              {:flow-id :fid-a1
+               :state {:a1 :A1, :a2 :A2}
+               :path
+               [{:flow-id :flow/start, :nsecs-delta :submap/ex, :count 1}
+                {:flow-id :fid-a2,     :nsecs-delta :submap/ex, :count 1}
+                {:flow-id :flow/end,   :nsecs-delta :submap/ex, :count 1}]}))]))])
+
 ;;;;
 
 #?(:cljs (test/run-tests))