W3C FAQ: Document character set http://www.w3.org/International/questions/qa-doc-charset

Unicode in XML & Other Markup Languages http://www.w3.org/TR/unicode-xml/

Authoring Techniques for XHTML & HTML Internationalization: Characters and Encodings http://www.w3.org/International/geo/html-tech/tech-character

Serving XHTML 1.0 http://www.w3.org/International/articles/serving-xhtml/

XHTML Media Types http://www.w3.org/TR/2002/NOTE-xhtml-media-types-20020801/

W3C FAQ: Unexpected characters or blank lines http://www.w3.org/International/questions/qa-utf8-bom

Other W3C I18N resources relating to characters & encoding http://www.w3.org/International/resource-index#charset