diff --git a/src/devtools/views/Components/Components.js b/src/devtools/views/Components/Components.js
index 3ed317a101..395087a21d 100644
--- a/src/devtools/views/Components/Components.js
+++ b/src/devtools/views/Components/Components.js
@@ -3,6 +3,7 @@
 import React, { Suspense } from 'react';
 import Tree from './Tree';
 import SelectedElement from './SelectedElement';
+import { HoveredElementContextController } from './HoveredElementContext';
 import { InspectedElementContextController } from './InspectedElementContext';
 import { OwnersListContextController } from './OwnersListContext';
 import portaledContent from '../portaledContent';
@@ -14,19 +15,21 @@ function Components(_: {||}) {
   // TODO Flex wrappers below should be user resizable.
   return (
     <OwnersListContextController>
-      <InspectedElementContextController>
-        <div className={styles.Components}>
-          <div className={styles.TreeWrapper}>
-            <Tree />
+      <HoveredElementContextController>
+        <InspectedElementContextController>
+          <div className={styles.Components}>
+            <div className={styles.TreeWrapper}>
+              <Tree />
+            </div>
+            <div className={styles.SelectedElementWrapper}>
+              <Suspense fallback={<Loading />}>
+                <SelectedElement />
+              </Suspense>
+            </div>
+            <ModalDialog />
           </div>
-          <div className={styles.SelectedElementWrapper}>
-            <Suspense fallback={<Loading />}>
-              <SelectedElement />
-            </Suspense>
-          </div>
-          <ModalDialog />
-        </div>
-      </InspectedElementContextController>
+        </InspectedElementContextController>
+      </HoveredElementContextController>
     </OwnersListContextController>
   );
 }
diff --git a/src/devtools/views/Components/Element.js b/src/devtools/views/Components/Element.js
index 0f3bb34a7a..020de1d5c8 100644
--- a/src/devtools/views/Components/Element.js
+++ b/src/devtools/views/Components/Element.js
@@ -19,6 +19,7 @@ import Store from 'src/devtools/store';
 import ButtonIcon from '../ButtonIcon';
 import { createRegExp } from '../utils';
 import { TreeDispatcherContext, TreeStateContext } from './TreeContext';
+import { HoveredElementSetIDContext } from './HoveredElementContext';
 import { StoreContext } from '../context';
 
 import type { ItemData } from './Tree';
@@ -38,6 +39,7 @@ export default function ElementView({ data, index, style }: Props) {
     TreeStateContext
   );
   const dispatch = useContext(TreeDispatcherContext);
+  const setHoveredElementID = useContext(HoveredElementSetIDContext);
 
   const element =
     ownerFlatTree !== null
@@ -119,9 +121,10 @@ export default function ElementView({ data, index, style }: Props) {
   const handleMouseEnter = useCallback(() => {
     setIsHovered(true);
     if (id !== null) {
+      setHoveredElementID(id);
       onElementMouseEnter(id);
     }
-  }, [onElementMouseEnter, id]);
+  }, [id, onElementMouseEnter, setHoveredElementID]);
 
   const handleMouseLeave = useCallback(() => {
     setIsHovered(false);
diff --git a/src/devtools/views/Components/Guidelines.css b/src/devtools/views/Components/Guidelines.css
new file mode 100644
index 0000000000..7ea56a3f50
--- /dev/null
+++ b/src/devtools/views/Components/Guidelines.css
@@ -0,0 +1,18 @@
+.GuidelineHovered,
+.GuidelineSelectedActive,
+.GuidelineSelectedInactive {
+  width: 1px;
+  z-index: 2;
+}
+
+.GuidelineHovered {
+  background-color: var(--color-guideline-hovered);
+}
+
+.GuidelineSelectedActive {
+  background-color: var(--color-background-selected);
+}
+
+.GuidelineSelectedInactive {
+  background-color: var(--color-background-inactive);
+}
diff --git a/src/devtools/views/Components/Guidelines.js b/src/devtools/views/Components/Guidelines.js
new file mode 100644
index 0000000000..f8397fd654
--- /dev/null
+++ b/src/devtools/views/Components/Guidelines.js
@@ -0,0 +1,126 @@
+// @flow
+
+import React, { Fragment, useContext, useMemo } from 'react';
+import { HoveredElementIDContext } from './HoveredElementContext';
+import { TreeStateContext } from './TreeContext';
+import TreeFocusedContext from './TreeFocusedContext';
+import { SettingsContext } from '../Settings/SettingsContext';
+import { StoreContext } from '../context';
+import { useSubscription } from '../hooks';
+import Store from '../../store';
+
+import styles from './Guidelines.css';
+
+export default function Guidelines(_: {||}) {
+  const hoveredElementID = useContext(HoveredElementIDContext);
+  const { selectedElementID } = useContext(TreeStateContext);
+  const treeFocused = useContext(TreeFocusedContext);
+
+  return (
+    <Fragment>
+      {hoveredElementID !== selectedElementID && (
+        <Guideline
+          className={styles.GuidelineHovered}
+          elementID={hoveredElementID}
+        />
+      )}
+      <Guideline
+        className={
+          treeFocused
+            ? styles.GuidelineSelectedActive
+            : styles.GuidelineSelectedInactive
+        }
+        elementID={selectedElementID}
+      />
+    </Fragment>
+  );
+}
+
+type Data = {|
+  depth: number,
+  startIndex: number,
+  stopIndex: number,
+|};
+
+type Props = {|
+  className: string,
+  elementID: number | null,
+|};
+
+function Guideline({ className, elementID }: Props) {
+  const store = useContext(StoreContext);
+  const { lineHeight } = useContext(SettingsContext);
+
+  const subscription = useMemo(
+    () => ({
+      getCurrentValue: () => {
+        if (elementID === null) {
+          return null;
+        }
+
+        const element = store.getElementByID(elementID);
+        if (
+          element === null ||
+          element.isCollapsed ||
+          element.children.length === 0
+        ) {
+          return null;
+        }
+
+        const startIndex = store.getIndexOfElementID(element.children[0]);
+        if (startIndex === null) {
+          return null;
+        }
+
+        let stopIndex = null;
+        let current = element;
+        while (current !== null) {
+          if (current.isCollapsed || current.children.length === 0) {
+            // We've found the last/deepest descendant.
+            stopIndex = store.getIndexOfElementID(current.id);
+            current = null;
+          } else {
+            const lastChildID = current.children[current.children.length - 1];
+            current = store.getElementByID(lastChildID);
+          }
+        }
+
+        if (stopIndex === null) {
+          return null;
+        }
+
+        return {
+          depth: element.depth,
+          startIndex,
+          stopIndex,
+        };
+      },
+      subscribe: (callback: Function) => {
+        store.addListener('mutated', callback);
+        return () => {
+          store.removeListener('mutated', callback);
+        };
+      },
+    }),
+    [elementID, store]
+  );
+  const data = useSubscription<Data | null, Store>(subscription);
+
+  if (data === null) {
+    return null;
+  }
+
+  const { depth, startIndex, stopIndex } = data;
+
+  return (
+    <div
+      className={className}
+      style={{
+        position: 'absolute',
+        top: `${startIndex * lineHeight}px`,
+        left: `${depth * 0.75 + 0.75}rem`,
+        height: `${(stopIndex + 1 - startIndex) * lineHeight}px`,
+      }}
+    />
+  );
+}
diff --git a/src/devtools/views/Components/HoveredElementContext.js b/src/devtools/views/Components/HoveredElementContext.js
new file mode 100644
index 0000000000..161fd1f620
--- /dev/null
+++ b/src/devtools/views/Components/HoveredElementContext.js
@@ -0,0 +1,34 @@
+// @flow
+
+import React, { createContext, useState } from 'react';
+
+type ID = number | null;
+type SetID = (id: ID) => void;
+
+const HoveredElementIDContext = createContext<ID>(null);
+HoveredElementIDContext.displayName = 'HoveredElementIDContext';
+
+const HoveredElementSetIDContext = createContext<SetID>(((null: any): SetID));
+HoveredElementSetIDContext.displayName = 'HoveredElementSetIDContext';
+
+type Props = {|
+  children: React$Node,
+|};
+
+function HoveredElementContextController({ children }: Props) {
+  const [hoveredElementID, setHoveredElementID] = useState<ID>(null);
+
+  return (
+    <HoveredElementIDContext.Provider value={hoveredElementID}>
+      <HoveredElementSetIDContext.Provider value={setHoveredElementID}>
+        {children}
+      </HoveredElementSetIDContext.Provider>
+    </HoveredElementIDContext.Provider>
+  );
+}
+
+export {
+  HoveredElementIDContext,
+  HoveredElementSetIDContext,
+  HoveredElementContextController,
+};
diff --git a/src/devtools/views/Components/Tree.js b/src/devtools/views/Components/Tree.js
index 4687c79939..0a6ac0fa4b 100644
--- a/src/devtools/views/Components/Tree.js
+++ b/src/devtools/views/Components/Tree.js
@@ -22,6 +22,9 @@ import SearchInput from './SearchInput';
 import { ComponentFiltersModalContextController } from './ComponentFiltersModalContext';
 import ToggleComponentFiltersModalButton from './ToggleComponentFiltersModalButton';
 import ComponentFiltersModal from './ComponentFiltersModal';
+import { HoveredElementSetIDContext } from './HoveredElementContext';
+import Guidelines from './Guidelines';
+import TreeFocusedContext from './TreeFocusedContext';
 
 import styles from './Tree.css';
 
@@ -273,54 +276,57 @@ export default function Tree(props: Props) {
   );
 
   return (
-    <ComponentFiltersModalContextController>
-      <div className={styles.Tree} ref={treeRef}>
-        <div className={styles.SearchInput}>
-          <InspectHostNodesToggle />
-          <div className={styles.VRule} />
-          <Suspense fallback={<Loading />}>
-            {ownerID !== null ? <OwnersStack /> : <SearchInput />}
-          </Suspense>
-          <div className={styles.VRule} />
-          <ToggleComponentFiltersModalButton />
+    <TreeFocusedContext.Provider value={treeFocused}>
+      <ComponentFiltersModalContextController>
+        <div className={styles.Tree} ref={treeRef}>
+          <div className={styles.SearchInput}>
+            <InspectHostNodesToggle />
+            <div className={styles.VRule} />
+            <Suspense fallback={<Loading />}>
+              {ownerID !== null ? <OwnersStack /> : <SearchInput />}
+            </Suspense>
+            <div className={styles.VRule} />
+            <ToggleComponentFiltersModalButton />
+          </div>
+          <div
+            className={styles.AutoSizerWrapper}
+            onBlur={handleBlur}
+            onFocus={handleFocus}
+            onKeyPress={handleKeyPress}
+            onMouseMove={handleMouseMove}
+            onMouseLeave={handleMouseLeave}
+            ref={focusTargetRef}
+            tabIndex={0}
+          >
+            <AutoSizer>
+              {({ height, width }) => (
+                // $FlowFixMe https://github.com/facebook/flow/issues/7341
+                <FixedSizeList
+                  className={styles.List}
+                  height={height}
+                  innerElementType={InnerElementType}
+                  itemCount={numElements}
+                  itemData={itemData}
+                  itemSize={lineHeight}
+                  overscanCount={3}
+                  ref={listRef}
+                  width={width}
+                >
+                  {ElementView}
+                </FixedSizeList>
+              )}
+            </AutoSizer>
+          </div>
+          <ComponentFiltersModal />
         </div>
-        <div
-          className={styles.AutoSizerWrapper}
-          onBlur={handleBlur}
-          onFocus={handleFocus}
-          onKeyPress={handleKeyPress}
-          onMouseMove={handleMouseMove}
-          onMouseLeave={handleMouseLeave}
-          ref={focusTargetRef}
-          tabIndex={0}
-        >
-          <AutoSizer>
-            {({ height, width }) => (
-              // $FlowFixMe https://github.com/facebook/flow/issues/7341
-              <FixedSizeList
-                className={styles.List}
-                height={height}
-                innerElementType={InnerElementType}
-                itemCount={numElements}
-                itemData={itemData}
-                itemSize={lineHeight}
-                overscanCount={3}
-                ref={listRef}
-                width={width}
-              >
-                {ElementView}
-              </FixedSizeList>
-            )}
-          </AutoSizer>
-        </div>
-        <ComponentFiltersModal />
-      </div>
-    </ComponentFiltersModalContextController>
+      </ComponentFiltersModalContextController>
+    </TreeFocusedContext.Provider>
   );
 }
 
-function InnerElementType({ style, ...rest }) {
+function InnerElementType({ children, style, ...rest }) {
   const { ownerID } = useContext(TreeStateContext);
+  const setHoveredElementID = useContext(HoveredElementSetIDContext);
 
   // The list may need to scroll horizontally due to deeply nested elements.
   // We don't know the maximum scroll width up front, because we're windowing.
@@ -355,6 +361,10 @@ function InnerElementType({ style, ...rest }) {
     setMinWidth(null);
   }
 
+  const handleMouseLeave = useCallback(() => {
+    setHoveredElementID(null);
+  }, [setHoveredElementID]);
+
   // This style override enables the background color to fill the full visible width,
   // when combined with the CSS tweaks in Element.
   // A lot of options were considered; this seemed the one that requires the least code.
@@ -362,6 +372,7 @@ function InnerElementType({ style, ...rest }) {
   return (
     <div
       className={styles.InnerElementType}
+      onMouseLeave={handleMouseLeave}
       style={{
         ...style,
         display: 'inline-block',
@@ -370,7 +381,10 @@ function InnerElementType({ style, ...rest }) {
       }}
       ref={divRef}
       {...rest}
-    />
+    >
+      <Guidelines />
+      {children}
+    </div>
   );
 }
 
diff --git a/src/devtools/views/Components/TreeFocusedContext.js b/src/devtools/views/Components/TreeFocusedContext.js
new file mode 100644
index 0000000000..7851db1316
--- /dev/null
+++ b/src/devtools/views/Components/TreeFocusedContext.js
@@ -0,0 +1,7 @@
+// @flow
+
+import { createContext } from 'react';
+
+const TreeFocusedContext = createContext<boolean>(false);
+
+export default TreeFocusedContext;
diff --git a/src/devtools/views/Settings/SettingsContext.js b/src/devtools/views/Settings/SettingsContext.js
index 17194aaa03..fa2be0f5be 100644
--- a/src/devtools/views/Settings/SettingsContext.js
+++ b/src/devtools/views/Settings/SettingsContext.js
@@ -261,6 +261,7 @@ function updateThemeVariables(
   updateStyleHelper(theme, 'color-dimmer', documentElements);
   updateStyleHelper(theme, 'color-dimmest', documentElements);
   updateStyleHelper(theme, 'color-expand-collapse-toggle', documentElements);
+  updateStyleHelper(theme, 'color-guideline-hovered', documentElements);
   updateStyleHelper(theme, 'color-jsx-arrow-brackets', documentElements);
   updateStyleHelper(
     theme,
diff --git a/src/devtools/views/root.css b/src/devtools/views/root.css
index 5dba64cc20..f0ec9588a0 100644
--- a/src/devtools/views/root.css
+++ b/src/devtools/views/root.css
@@ -42,6 +42,7 @@
   --light-color-dimmer: #cfd1d5;
   --light-color-dimmest: #eff0f1;
   --light-color-expand-collapse-toggle: #777d88;
+  --light-color-guideline-hovered: rgba(0, 0, 0, 0.1);
   --light-color-jsx-arrow-brackets: #333333;
   --light-color-jsx-arrow-brackets-inverted: rgba(255, 255, 255, 0.7);
   --light-color-modal-background: rgba(255, 255, 255, 0.75);
@@ -99,6 +100,7 @@
   --dark-color-dimmer: #777d88;
   --dark-color-dimmest: #4f5766;
   --dark-color-expand-collapse-toggle: #8f949d;
+  --dark-color-guideline-hovered: rgba(255, 255, 255, 0.1);
   --dark-color-jsx-arrow-brackets: #777d88;
   --dark-color-jsx-arrow-brackets-inverted: rgba(255, 255, 255, 0.7);
   --dark-color-modal-background: rgba(0, 0, 0, 0.75);