diff --git a/Userland/Libraries/LibWeb/DOM/Element.cpp b/Userland/Libraries/LibWeb/DOM/Element.cpp
index 9f420bb5c1..583689cfbc 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Element.cpp
@@ -17,6 +17,7 @@
 #include <LibWeb/DOM/HTMLCollection.h>
 #include <LibWeb/DOM/ShadowRoot.h>
 #include <LibWeb/DOM/Text.h>
+#include <LibWeb/DOMParsing/InnerHTML.h>
 #include <LibWeb/HTML/EventLoop/EventLoop.h>
 #include <LibWeb/HTML/Parser/HTMLDocumentParser.h>
 #include <LibWeb/Layout/BlockBox.h>
@@ -244,16 +245,15 @@ NonnullRefPtr<CSS::StyleProperties> Element::computed_style()
     return properties;
 }
 
-void Element::set_inner_html(StringView markup)
+ExceptionOr<void> Element::set_inner_html(String const& markup)
 {
-    auto new_children = HTML::HTMLDocumentParser::parse_html_fragment(*this, markup);
-    remove_all_children();
-    while (!new_children.is_empty()) {
-        append_child(new_children.take_first());
-    }
+    auto result = DOMParsing::InnerHTML::inner_html_setter(*this, markup);
+    if (result.is_exception())
+        return result.exception();
 
     set_needs_style_update(true);
     document().invalidate_layout();
+    return {};
 }
 
 // https://w3c.github.io/DOM-Parsing/#dom-innerhtml-innerhtml
diff --git a/Userland/Libraries/LibWeb/DOM/Element.h b/Userland/Libraries/LibWeb/DOM/Element.h
index 4d54e2ab57..e1eb9369e4 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.h
+++ b/Userland/Libraries/LibWeb/DOM/Element.h
@@ -81,9 +81,8 @@ public:
 
     NonnullRefPtr<CSS::CSSStyleDeclaration> style_for_bindings();
 
-    // FIXME: innerHTML also appears on shadow roots. https://w3c.github.io/DOM-Parsing/#dom-innerhtml
     String inner_html() const;
-    void set_inner_html(StringView);
+    ExceptionOr<void> set_inner_html(String const&);
 
     bool is_focused() const;
     virtual bool is_focusable() const { return false; }
diff --git a/Userland/Libraries/LibWeb/DOM/Element.idl b/Userland/Libraries/LibWeb/DOM/Element.idl
index 536c4120e9..031e8d94d4 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.idl
+++ b/Userland/Libraries/LibWeb/DOM/Element.idl
@@ -13,7 +13,9 @@ interface Element : Node {
     HTMLCollection getElementsByTagName(DOMString tagName);
     HTMLCollection getElementsByClassName(DOMString className);
 
-    [LegacyNullToEmptyString] attribute DOMString innerHTML;
+    // FIXME: This should come from a InnerHTML mixin.
+    [LegacyNullToEmptyString, CEReactions] attribute DOMString innerHTML;
+
     [Reflect] attribute DOMString id;
     [Reflect=class] attribute DOMString className;
 
diff --git a/Userland/Libraries/LibWeb/DOM/ShadowRoot.cpp b/Userland/Libraries/LibWeb/DOM/ShadowRoot.cpp
index 7043ce8242..675a8a2df2 100644
--- a/Userland/Libraries/LibWeb/DOM/ShadowRoot.cpp
+++ b/Userland/Libraries/LibWeb/DOM/ShadowRoot.cpp
@@ -4,8 +4,10 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/Event.h>
 #include <LibWeb/DOM/ShadowRoot.h>
+#include <LibWeb/DOMParsing/InnerHTML.h>
 #include <LibWeb/Layout/BlockBox.h>
 
 namespace Web::DOM {
@@ -33,4 +35,22 @@ RefPtr<Layout::Node> ShadowRoot::create_layout_node()
     return adopt_ref(*new Layout::BlockBox(document(), this, CSS::ComputedValues {}));
 }
 
+// https://w3c.github.io/DOM-Parsing/#dom-innerhtml-innerhtml
+String ShadowRoot::inner_html() const
+{
+    return serialize_fragment(/* FIXME: Providing true for the require well-formed flag (which may throw) */);
+}
+
+// https://w3c.github.io/DOM-Parsing/#dom-innerhtml-innerhtml
+ExceptionOr<void> ShadowRoot::set_inner_html(String const& markup)
+{
+    auto result = DOMParsing::InnerHTML::inner_html_setter(*this, markup);
+    if (result.is_exception())
+        return result.exception();
+
+    set_needs_style_update(true);
+    document().invalidate_layout();
+    return {};
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/DOM/ShadowRoot.h b/Userland/Libraries/LibWeb/DOM/ShadowRoot.h
index 22cc1a1db7..12532a8eda 100644
--- a/Userland/Libraries/LibWeb/DOM/ShadowRoot.h
+++ b/Userland/Libraries/LibWeb/DOM/ShadowRoot.h
@@ -28,6 +28,9 @@ public:
     // NOTE: This is intended for the JS bindings.
     String mode() const { return m_closed ? "closed" : "open"; }
 
+    String inner_html() const;
+    ExceptionOr<void> set_inner_html(String const&);
+
 private:
     // ^Node
     virtual FlyString node_name() const override { return "#shadow-root"; }
diff --git a/Userland/Libraries/LibWeb/DOM/ShadowRoot.idl b/Userland/Libraries/LibWeb/DOM/ShadowRoot.idl
index 320ca53e80..ea228c9aa8 100644
--- a/Userland/Libraries/LibWeb/DOM/ShadowRoot.idl
+++ b/Userland/Libraries/LibWeb/DOM/ShadowRoot.idl
@@ -3,4 +3,7 @@ interface ShadowRoot : DocumentFragment {
     readonly attribute DOMString mode;
     readonly attribute Element host;
 
+    // FIXME: This should come from a InnerHTML mixin.
+    [LegacyNullToEmptyString] attribute DOMString innerHTML;
+
 };
diff --git a/Userland/Libraries/LibWeb/DOMParsing/Algorithms.h b/Userland/Libraries/LibWeb/DOMParsing/Algorithms.h
new file mode 100644
index 0000000000..0a04654bba
--- /dev/null
+++ b/Userland/Libraries/LibWeb/DOMParsing/Algorithms.h
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/DOM/DocumentFragment.h>
+#include <LibWeb/DOM/ExceptionOr.h>
+#include <LibWeb/HTML/Parser/HTMLDocumentParser.h>
+
+namespace Web::DOMParsing {
+
+// https://w3c.github.io/DOM-Parsing/#dfn-fragment-parsing-algorithm
+static DOM::ExceptionOr<NonnullRefPtr<DOM::DocumentFragment>> parse_fragment(String const& markup, DOM::Element& context_element)
+{
+    // FIXME: Handle XML documents.
+
+    auto new_children = HTML::HTMLDocumentParser::parse_html_fragment(context_element, markup);
+    auto fragment = make_ref_counted<DOM::DocumentFragment>(context_element.document());
+
+    for (auto& child : new_children) {
+        // I don't know if this can throw here, but let's be safe.
+        auto result = fragment->append_child(child);
+        if (result.is_exception())
+            return result.exception();
+    }
+
+    return fragment;
+}
+
+}
diff --git a/Userland/Libraries/LibWeb/DOMParsing/InnerHTML.h b/Userland/Libraries/LibWeb/DOMParsing/InnerHTML.h
new file mode 100644
index 0000000000..ef95a21e4d
--- /dev/null
+++ b/Userland/Libraries/LibWeb/DOMParsing/InnerHTML.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/DOM/Element.h>
+#include <LibWeb/DOM/ExceptionOr.h>
+#include <LibWeb/DOM/ShadowRoot.h>
+#include <LibWeb/DOMParsing/Algorithms.h>
+#include <LibWeb/HTML/HTMLTemplateElement.h>
+
+namespace Web::DOMParsing::InnerHTML {
+
+// https://w3c.github.io/DOM-Parsing/#dom-innerhtml-innerhtml
+static DOM::ExceptionOr<void> inner_html_setter(NonnullRefPtr<DOM::Node> context_object, String const& value)
+{
+    // 1. Let context element be the context object's host if the context object is a ShadowRoot object, or the context object otherwise.
+    //    (This is handled in Element and ShadowRoot)
+    NonnullRefPtr<DOM::Element> context_element = is<DOM::ShadowRoot>(*context_object) ? *verify_cast<DOM::ShadowRoot>(*context_object).host() : verify_cast<DOM::Element>(*context_object);
+
+    // 2. Let fragment be the result of invoking the fragment parsing algorithm with the new value as markup, and with context element.
+    auto fragment_or_exception = parse_fragment(value, context_element);
+    if (fragment_or_exception.is_exception())
+        return fragment_or_exception.exception();
+    auto fragment = fragment_or_exception.release_value();
+
+    // 3. If the context object is a template element, then let context object be the template's template contents (a DocumentFragment).
+    if (is<HTML::HTMLTemplateElement>(*context_object))
+        context_object = verify_cast<HTML::HTMLTemplateElement>(*context_object).content();
+
+    // 4. Replace all with fragment within the context object.
+    context_object->replace_all(fragment);
+
+    return {};
+}
+
+}