 <p>Look at the Unicode <a href="http://www.fileformat.info/info/unicode/category/index.htm" rel="nofollow noreferrer">character categories</a>. You can match these in C# regular expressions with the character class syntax <code>\p{catname}</code>. So to match a lower-case letter, you would use <code>\p{Ll}</code>. You can combine these. <code>[\p{Ll}\p{Lu}]</code> matches characters in either the Ll or Lu class.</p>