diff --git a/AK/String.h b/AK/String.h
index 1a19b6f429c..7bcf722a476 100644
--- a/AK/String.h
+++ b/AK/String.h
@@ -49,6 +49,10 @@ public:
     ErrorOr<String> to_lowercase(Optional<StringView> const& locale = {}) const;
     ErrorOr<String> to_uppercase(Optional<StringView> const& locale = {}) const;
     ErrorOr<String> to_titlecase(Optional<StringView> const& locale = {}) const;
+    ErrorOr<String> to_casefold() const;
+
+    // Compare this String against another string with caseless matching. Using this method requires linking LibUnicode into your application.
+    ErrorOr<bool> equals_ignoring_case(String const&) const;
 
     // Creates a substring with a deep copy of the specified data window.
     ErrorOr<String> substring_from_byte_offset(size_t start, size_t byte_count) const;
diff --git a/Tests/AK/TestString.cpp b/Tests/AK/TestString.cpp
index 42f5ffc63f9..d78854b6269 100644
--- a/Tests/AK/TestString.cpp
+++ b/Tests/AK/TestString.cpp
@@ -187,6 +187,66 @@ TEST_CASE(to_titlecase)
     }
 }
 
+TEST_CASE(equals_ignoring_case)
+{
+    {
+        String string1 {};
+        String string2 {};
+
+        EXPECT(MUST(string1.equals_ignoring_case(string2)));
+    }
+    {
+        auto string1 = MUST(String::from_utf8("abcd"sv));
+        auto string2 = MUST(String::from_utf8("ABCD"sv));
+        auto string3 = MUST(String::from_utf8("AbCd"sv));
+        auto string4 = MUST(String::from_utf8("dcba"sv));
+
+        EXPECT(MUST(string1.equals_ignoring_case(string2)));
+        EXPECT(MUST(string1.equals_ignoring_case(string3)));
+        EXPECT(!MUST(string1.equals_ignoring_case(string4)));
+
+        EXPECT(MUST(string2.equals_ignoring_case(string1)));
+        EXPECT(MUST(string2.equals_ignoring_case(string3)));
+        EXPECT(!MUST(string2.equals_ignoring_case(string4)));
+
+        EXPECT(MUST(string3.equals_ignoring_case(string1)));
+        EXPECT(MUST(string3.equals_ignoring_case(string2)));
+        EXPECT(!MUST(string3.equals_ignoring_case(string4)));
+    }
+    {
+        auto string1 = MUST(String::from_utf8("\u00DF"sv)); // LATIN SMALL LETTER SHARP S
+        auto string2 = MUST(String::from_utf8("SS"sv));
+        auto string3 = MUST(String::from_utf8("Ss"sv));
+        auto string4 = MUST(String::from_utf8("ss"sv));
+        auto string5 = MUST(String::from_utf8("S"sv));
+        auto string6 = MUST(String::from_utf8("s"sv));
+
+        EXPECT(MUST(string1.equals_ignoring_case(string2)));
+        EXPECT(MUST(string1.equals_ignoring_case(string3)));
+        EXPECT(MUST(string1.equals_ignoring_case(string4)));
+        EXPECT(!MUST(string1.equals_ignoring_case(string5)));
+        EXPECT(!MUST(string1.equals_ignoring_case(string6)));
+
+        EXPECT(MUST(string2.equals_ignoring_case(string1)));
+        EXPECT(MUST(string2.equals_ignoring_case(string3)));
+        EXPECT(MUST(string2.equals_ignoring_case(string4)));
+        EXPECT(!MUST(string2.equals_ignoring_case(string5)));
+        EXPECT(!MUST(string2.equals_ignoring_case(string6)));
+
+        EXPECT(MUST(string3.equals_ignoring_case(string1)));
+        EXPECT(MUST(string3.equals_ignoring_case(string2)));
+        EXPECT(MUST(string3.equals_ignoring_case(string4)));
+        EXPECT(!MUST(string3.equals_ignoring_case(string5)));
+        EXPECT(!MUST(string3.equals_ignoring_case(string6)));
+
+        EXPECT(MUST(string4.equals_ignoring_case(string1)));
+        EXPECT(MUST(string4.equals_ignoring_case(string2)));
+        EXPECT(MUST(string4.equals_ignoring_case(string3)));
+        EXPECT(!MUST(string4.equals_ignoring_case(string5)));
+        EXPECT(!MUST(string4.equals_ignoring_case(string6)));
+    }
+}
+
 TEST_CASE(is_one_of)
 {
     auto foo = MUST(String::from_utf8("foo"sv));
diff --git a/Userland/Libraries/LibUnicode/String.cpp b/Userland/Libraries/LibUnicode/String.cpp
index 5251d310bd9..e198058a706 100644
--- a/Userland/Libraries/LibUnicode/String.cpp
+++ b/Userland/Libraries/LibUnicode/String.cpp
@@ -33,4 +33,19 @@ ErrorOr<String> String::to_titlecase(Optional<StringView> const& locale) const
     return builder.to_string();
 }
 
+ErrorOr<String> String::to_casefold() const
+{
+    StringBuilder builder;
+    TRY(Unicode::Detail::build_casefold_string(code_points(), builder));
+    return builder.to_string();
+}
+
+// https://www.unicode.org/versions/Unicode15.0.0/ch03.pdf#G34145
+ErrorOr<bool> String::equals_ignoring_case(String const& other) const
+{
+    // A string X is a caseless match for a string Y if and only if:
+    //     toCasefold(X) = toCasefold(Y)
+    return TRY(to_casefold()) == TRY(other.to_casefold());
+}
+
 }