diff --git a/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp b/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp
index 5775335d9b..80ec6fb56f 100644
--- a/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp
+++ b/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp
@@ -10,6 +10,7 @@
 #include <AK/Optional.h>
 #include <AK/Result.h>
 #include <AK/TemporaryChange.h>
+#include <AK/Utf16View.h>
 #include <LibJS/Interpreter.h>
 #include <LibJS/Parser.h>
 #include <LibJS/Runtime/AbstractOperations.h>
@@ -583,36 +584,51 @@ String get_substitution(GlobalObject& global_object, String const& matched, Stri
     if (vm.exception())
         return {};
 
+    // FIXME: Once RegExp.prototype supports UTF-16, this AO can take UTF-16 strings as parameters instead of having to transcode here.
+    auto utf16_matched = AK::utf8_to_utf16(matched);
+    auto match_length = utf16_matched.size();
+
+    auto utf16_string = AK::utf8_to_utf16(str);
+    Utf16View utf16_string_view { utf16_string };
+    auto string_length = utf16_string_view.length_in_code_units();
+
+    auto utf16_replace = AK::utf8_to_utf16(replace_string);
+    Utf16View utf16_replace_view { utf16_replace };
+    auto replace_length = utf16_replace_view.length_in_code_units();
+
     StringBuilder result;
 
-    for (size_t i = 0; i < replace_string.length(); ++i) {
-        char curr = replace_string[i];
+    for (size_t i = 0; i < replace_length; ++i) {
+        u16 curr = utf16_replace_view.code_unit_at(i);
 
-        if ((curr != '$') || (i + 1 >= replace_string.length())) {
+        if ((curr != '$') || (i + 1 >= replace_length)) {
             result.append(curr);
             continue;
         }
 
-        char next = replace_string[i + 1];
+        u16 next = utf16_replace_view.code_unit_at(i + 1);
 
         if (next == '$') {
-            result.append(next);
+            result.append('$');
             ++i;
         } else if (next == '&') {
             result.append(matched);
             ++i;
         } else if (next == '`') {
-            result.append(str.substring_view(0, position));
+            auto substring = utf16_string_view.substring_view(0, position);
+            result.append(substring.to_utf8(Utf16View::AllowInvalidCodeUnits::Yes));
             ++i;
         } else if (next == '\'') {
-            auto tail_pos = position + matched.length();
-            if (tail_pos < str.length())
-                result.append(str.substring_view(tail_pos));
+            auto tail_pos = position + match_length;
+            if (tail_pos < string_length) {
+                auto substring = utf16_string_view.substring_view(tail_pos);
+                result.append(substring.to_utf8(Utf16View::AllowInvalidCodeUnits::Yes));
+            }
             ++i;
         } else if (is_ascii_digit(next)) {
-            bool is_two_digits = (i + 2 < replace_string.length()) && is_ascii_digit(replace_string[i + 2]);
+            bool is_two_digits = (i + 2 < replace_length) && is_ascii_digit(utf16_replace_view.code_unit_at(i + 2));
 
-            auto capture_postition_string = replace_string.substring_view(i + 1, is_two_digits ? 2 : 1);
+            auto capture_postition_string = utf16_replace_view.substring_view(i + 1, is_two_digits ? 2 : 1).to_utf8();
             auto capture_position = capture_postition_string.to_uint();
 
             if (capture_position.has_value() && (*capture_position > 0) && (*capture_position <= captures.size())) {
@@ -632,12 +648,20 @@ String get_substitution(GlobalObject& global_object, String const& matched, Stri
             }
         } else if (next == '<') {
             auto start_position = i + 2;
-            auto end_position = replace_string.find('>', start_position);
+            Optional<size_t> end_position;
+
+            for (size_t j = start_position; j < replace_length; ++j) {
+                if (utf16_replace_view.code_unit_at(j) == '>') {
+                    end_position = j;
+                    break;
+                }
+            }
 
             if (named_captures.is_undefined() || !end_position.has_value()) {
                 result.append(curr);
             } else {
-                auto group_name = replace_string.substring(start_position, *end_position - start_position);
+                auto group_name_view = utf16_replace_view.substring_view(start_position, *end_position - start_position);
+                auto group_name = group_name_view.to_utf8(Utf16View::AllowInvalidCodeUnits::Yes);
 
                 auto capture = named_captures.as_object().get(group_name);
                 if (vm.exception())
diff --git a/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp b/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp
index 8112b7d145..f98e93ec20 100644
--- a/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp
@@ -903,24 +903,29 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::replace)
         return {};
 
     if (!replace_value.is_function()) {
-        auto replace_string = replace_value.to_string(global_object);
+        auto replace_string = replace_value.to_utf16_string(global_object);
         if (vm.exception())
             return {};
-
-        replace_value = js_string(vm, move(replace_string));
+        replace_value = js_string(vm, Utf16View { replace_string });
         if (vm.exception())
             return {};
     }
 
-    Optional<size_t> position = string.find(search_string);
-    if (!position.has_value())
-        return js_string(vm, string);
+    auto utf16_string = AK::utf8_to_utf16(string);
+    Utf16View utf16_string_view { utf16_string };
 
-    auto preserved = string.substring(0, position.value());
+    auto utf16_search_string = AK::utf8_to_utf16(search_string);
+    Utf16View utf16_search_view { utf16_search_string };
+
+    Optional<size_t> position = string_index_of(utf16_string_view, utf16_search_view, 0);
+    if (!position.has_value())
+        return js_string(vm, utf16_string_view);
+
+    auto preserved = utf16_string_view.substring_view(0, position.value());
     String replacement;
 
     if (replace_value.is_function()) {
-        auto result = vm.call(replace_value.as_function(), js_undefined(), js_string(vm, search_string), Value(position.value()), js_string(vm, string));
+        auto result = vm.call(replace_value.as_function(), js_undefined(), js_string(vm, utf16_search_view), Value(position.value()), js_string(vm, utf16_string_view));
         if (vm.exception())
             return {};
 
@@ -933,10 +938,12 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::replace)
             return {};
     }
 
+    utf16_string_view = utf16_string_view.substring_view(*position + utf16_search_view.length_in_code_units());
+
     StringBuilder builder;
-    builder.append(preserved);
+    builder.append(preserved.to_utf8(Utf16View::AllowInvalidCodeUnits::Yes));
     builder.append(replacement);
-    builder.append(string.substring(position.value() + search_string.length()));
+    builder.append(utf16_string_view.to_utf8(Utf16View::AllowInvalidCodeUnits::Yes));
 
     return js_string(vm, builder.build());
 }
diff --git a/Userland/Libraries/LibJS/Tests/builtins/String/String.prototype.replace.js b/Userland/Libraries/LibJS/Tests/builtins/String/String.prototype.replace.js
index 446ff62816..b61c0e77e2 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/String/String.prototype.replace.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/String/String.prototype.replace.js
@@ -232,3 +232,13 @@ test("override exec with non-function", () => {
     re.exec = 3;
     expect("test".replace(re, "x")).toBe("x");
 });
+
+test("UTF-16", () => {
+    expect("😀".replace("😀", "")).toBe("");
+    expect("😀".replace("\ud83d", "")).toBe("\ude00");
+    expect("😀".replace("\ude00", "")).toBe("\ud83d");
+
+    // FIXME: RegExp.prototype [ @@replace ] also needs to support UTF-16.
+    // expect("😀".replace(/\ud83d/, "")).toBe("\ude00");
+    // expect("😀".replace(/\ude00/, "")).toBe("\ud83d");
+});