diff --git a/src/Illuminate/Support/Str.php b/src/Illuminate/Support/Str.php
index 0d706d1920ca..a4e14666587e 100644
--- a/src/Illuminate/Support/Str.php
+++ b/src/Illuminate/Support/Str.php
@@ -284,6 +284,19 @@ public static function containsAll($haystack, $needles, $ignoreCase = false)
         return true;
     }
 
+    /**
+     * Convert the case of a string.
+     *
+     * @param  string  $string
+     * @param  int  $mode
+     * @param  string  $encoding
+     * @return string
+     */
+    public static function convertCase(string $string, int $mode = MB_CASE_FOLD, ?string $encoding = 'UTF-8')
+    {
+        return mb_convert_case($string, $mode, $encoding);
+    }
+
     /**
      * Determine if a given string ends with a given substring.
      *