Just five: < (<), & (&), > (>), " ("), and ' ('). For normal text (not markup), there are no special characters except < and &: just make sure your XML Declaration refers to the correct encoding scheme for the language and/or writing system you want to use, and that your computer correctly stores the file using that encoding scheme. See the question on non-Latin characters for a longer explanation. Apart from the invisible ASCII control characters (the ones you can't type), all other characters are just normal text. Currency signs (€, £, $, ƒ, ₨, Ƀ, and others), all the punctuation (except < and &), and all other letters, signs, and symbols in any language or writing system are just text (assuming you have the correct character encoding). If your keyboard will not allow you to type the characters you want, or if you want to use characters outside the limits of the encoding scheme you have chosen, you can...