diff --git a/Tests/LibWeb/Text/expected/document-adopted-style-sheets.txt b/Tests/LibWeb/Text/expected/document-adopted-style-sheets.txt
new file mode 100644
index 0000000000..493750a428
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/document-adopted-style-sheets.txt
@@ -0,0 +1,11 @@
+  color with no adopted style sheets: rgb(0, 0, 0)
+document.adoptedStyleSheets.length=(1)
+add style sheet using Array.prototype.push(): rgb(255, 0, 0)
+document.adoptedStyleSheets.length=(0)
+delete added style sheet using Array.prototype.pop(): rgb(0, 0, 0)
+document.adoptedStyleSheets.length=(1)
+add style by assigning array to document.adoptedStyleSheets: rgb(255, 0, 0)
+document.adoptedStyleSheets.length=(1)
+add style by assigning Set to document.adoptedStyleSheets: rgb(0, 128, 0)
+assignment of non-iterable value to document.adoptedStyleSheets throws "1 is not iterable"
+assignment of value that is not CSSStyleSheet throws "Not an object of type CSSStyleSheet"
diff --git a/Tests/LibWeb/Text/input/document-adopted-style-sheets.html b/Tests/LibWeb/Text/input/document-adopted-style-sheets.html
new file mode 100644
index 0000000000..f8bc245bd9
--- /dev/null
+++ b/Tests/LibWeb/Text/input/document-adopted-style-sheets.html
@@ -0,0 +1,72 @@
+<script src="include.js"></script>
+<div id="testElement"></div>
+<script>
+    test(() => {
+        // Make sure assignment of empty array works correctly
+        document.adoptedStyleSheets = [];
+
+        {
+            const computedStyle = window.getComputedStyle(testElement);
+            const color = computedStyle.getPropertyValue("color");
+            println(`color with no adopted style sheets: ${color}`);
+        }
+
+        const sheetColorRed = new CSSStyleSheet();
+        sheetColorRed.replaceSync("#testElement { color: red }");
+        document.adoptedStyleSheets.push(sheetColorRed);
+
+        println(`document.adoptedStyleSheets.length=(${document.adoptedStyleSheets.length})`);
+
+        {
+            const computedStyle = window.getComputedStyle(testElement);
+            const color = computedStyle.getPropertyValue("color");
+            println(`add style sheet using Array.prototype.push(): ${color}`);
+        }
+
+        document.adoptedStyleSheets.pop();
+
+        println(`document.adoptedStyleSheets.length=(${document.adoptedStyleSheets.length})`);
+
+        {
+            const computedStyle = window.getComputedStyle(testElement);
+            const color = computedStyle.getPropertyValue("color");
+            println(`delete added style sheet using Array.prototype.pop(): ${color}`);
+        }
+
+        document.adoptedStyleSheets = [sheetColorRed];
+
+        println(`document.adoptedStyleSheets.length=(${document.adoptedStyleSheets.length})`);
+
+        {
+            const computedStyle = window.getComputedStyle(testElement);
+            const color = computedStyle.getPropertyValue("color");
+            println(`add style by assigning array to document.adoptedStyleSheets: ${color}`);
+        }
+
+        const sheetColorGreen = new CSSStyleSheet();
+        sheetColorGreen.replaceSync("#testElement { color: green }");
+        document.adoptedStyleSheets.push(sheetColorGreen);
+
+        document.adoptedStyleSheets = new Set([sheetColorGreen]);
+
+        println(`document.adoptedStyleSheets.length=(${document.adoptedStyleSheets.length})`);
+
+        {
+            const computedStyle = window.getComputedStyle(testElement);
+            const color = computedStyle.getPropertyValue("color");
+            println(`add style by assigning Set to document.adoptedStyleSheets: ${color}`);
+        }
+
+        try {
+            document.adoptedStyleSheets = 1;
+        } catch(err) {
+            println(`assignment of non-iterable value to document.adoptedStyleSheets throws "${err.message}"`);
+        }
+
+        try {
+            document.adoptedStyleSheets = ["foo"];
+        } catch(err) {
+            println(`assignment of value that is not CSSStyleSheet throws "${err.message}"`);
+        }
+    });
+</script>
diff --git a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
index 4942f76400..b959e5f17f 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -266,8 +266,9 @@ void StyleComputer::for_each_stylesheet(CascadeOrigin cascade_origin, Callback c
             callback(*m_user_style_sheet);
     }
     if (cascade_origin == CascadeOrigin::Author) {
-        for (auto const& sheet : document().style_sheets().sheets())
-            callback(*sheet);
+        document().for_each_css_style_sheet([&](CSSStyleSheet& sheet) {
+            callback(sheet);
+        });
     }
 }
 
diff --git a/Userland/Libraries/LibWeb/DOM/Document.cpp b/Userland/Libraries/LibWeb/DOM/Document.cpp
index 2eebc56413..89a7e11d1c 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Document.cpp
@@ -483,6 +483,8 @@ void Document::visit_edges(Cell::Visitor& visitor)
         visitor.visit(event.event);
         visitor.visit(event.target);
     }
+
+    visitor.visit(m_adopted_style_sheets);
 }
 
 // https://w3c.github.io/selection-api/#dom-document-getselection
@@ -4562,4 +4564,78 @@ bool Document::has_skipped_resize_observations()
     return false;
 }
 
+static JS::NonnullGCPtr<WebIDL::ObservableArray> create_adopted_style_sheets_list(Document& document)
+{
+    auto adopted_style_sheets = WebIDL::ObservableArray::create(document.realm());
+    adopted_style_sheets->set_on_set_an_indexed_value_callback([&document](JS::Value& value) -> WebIDL::ExceptionOr<void> {
+        auto& vm = document.vm();
+        if (!value.is_object())
+            return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotAnObjectOfType, "CSSStyleSheet");
+        auto& object = value.as_object();
+        if (!is<CSS::CSSStyleSheet>(object))
+            return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotAnObjectOfType, "CSSStyleSheet");
+        auto& style_sheet = static_cast<CSS::CSSStyleSheet&>(object);
+
+        // The set an indexed value algorithm for adoptedStyleSheets, given value and index, is the following:
+        // 1. If value’s constructed flag is not set, or its constructor document is not equal to this
+        //    DocumentOrShadowRoot's node document, throw a "NotAllowedError" DOMException.
+        if (!style_sheet.constructed())
+            return WebIDL::NotAllowedError::create(document.realm(), "StyleSheet's constructed flag is not set."_fly_string);
+        if (!style_sheet.constructed() || style_sheet.constructor_document().ptr() != &document)
+            return WebIDL::NotAllowedError::create(document.realm(), "Sharing a StyleSheet between documents is not allowed."_fly_string);
+
+        document.style_computer().load_fonts_from_sheet(style_sheet);
+        document.style_computer().invalidate_rule_cache();
+        document.invalidate_style();
+        return {};
+    });
+    adopted_style_sheets->set_on_delete_an_indexed_value_callback([&document]() -> WebIDL::ExceptionOr<void> {
+        document.style_computer().invalidate_rule_cache();
+        document.invalidate_style();
+        return {};
+    });
+
+    return adopted_style_sheets;
+}
+
+JS::NonnullGCPtr<WebIDL::ObservableArray> Document::adopted_style_sheets() const
+{
+    if (!m_adopted_style_sheets)
+        m_adopted_style_sheets = create_adopted_style_sheets_list(const_cast<Document&>(*this));
+    return *m_adopted_style_sheets;
+}
+
+WebIDL::ExceptionOr<void> Document::set_adopted_style_sheets(JS::Value new_value)
+{
+    if (!m_adopted_style_sheets)
+        m_adopted_style_sheets = create_adopted_style_sheets_list(const_cast<Document&>(*this));
+
+    m_adopted_style_sheets->clear();
+    auto iterator_record = TRY(get_iterator(vm(), new_value, JS::IteratorHint::Sync));
+    while (true) {
+        auto next = TRY(iterator_step_value(vm(), iterator_record));
+        if (!next.has_value())
+            break;
+        TRY(m_adopted_style_sheets->append(*next));
+    }
+
+    return {};
+}
+
+void Document::for_each_css_style_sheet(Function<void(CSS::CSSStyleSheet&)>&& callback) const
+{
+    for (auto& style_sheet : m_style_sheets->sheets())
+        callback(*style_sheet);
+
+    if (m_adopted_style_sheets) {
+        for (auto& entry : m_adopted_style_sheets->indexed_properties()) {
+            auto value_and_attributes = m_adopted_style_sheets->indexed_properties().storage()->get(entry.index());
+            if (value_and_attributes.has_value()) {
+                auto& style_sheet = verify_cast<CSS::CSSStyleSheet>(value_and_attributes->value.as_object());
+                callback(style_sheet);
+            }
+        }
+    }
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/DOM/Document.h b/Userland/Libraries/LibWeb/DOM/Document.h
index 530ca53522..b5f9c14041 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.h
+++ b/Userland/Libraries/LibWeb/DOM/Document.h
@@ -34,6 +34,7 @@
 #include <LibWeb/HTML/SharedImageRequest.h>
 #include <LibWeb/HTML/VisibilityState.h>
 #include <LibWeb/WebIDL/ExceptionOr.h>
+#include <LibWeb/WebIDL/ObservableArray.h>
 
 namespace Web::DOM {
 
@@ -131,6 +132,8 @@ public:
     CSS::StyleSheetList& style_sheets();
     CSS::StyleSheetList const& style_sheets() const;
 
+    void for_each_css_style_sheet(Function<void(CSS::CSSStyleSheet&)>&& callback) const;
+
     CSS::StyleSheetList* style_sheets_for_bindings() { return &style_sheets(); }
 
     virtual FlyString node_name() const override { return "#document"_fly_string; }
@@ -598,6 +601,9 @@ public:
     [[nodiscard]] bool has_active_resize_observations();
     [[nodiscard]] bool has_skipped_resize_observations();
 
+    JS::NonnullGCPtr<WebIDL::ObservableArray> adopted_style_sheets() const;
+    WebIDL::ExceptionOr<void> set_adopted_style_sheets(JS::Value);
+
 protected:
     virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
@@ -832,6 +838,8 @@ private:
     bool m_design_mode_enabled { false };
 
     bool m_needs_to_resolve_paint_only_properties { true };
+
+    mutable JS::GCPtr<WebIDL::ObservableArray> m_adopted_style_sheets;
 };
 
 template<>
diff --git a/Userland/Libraries/LibWeb/DOM/Document.idl b/Userland/Libraries/LibWeb/DOM/Document.idl
index 5054da003d..c00419ea27 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.idl
+++ b/Userland/Libraries/LibWeb/DOM/Document.idl
@@ -95,6 +95,7 @@ interface Document : Node {
     [CEReactions, ImplementedAs=adopt_node_binding] Node adoptNode(Node node);
 
     [ImplementedAs=style_sheets_for_bindings] readonly attribute StyleSheetList styleSheets;
+    attribute any adoptedStyleSheets;
 
     readonly attribute DOMString compatMode;
     readonly attribute DocumentType? doctype;