Tutorial: Character sets & encodings in XHTML, HTML and CSS

If a user agent (eg. a browser) is unable to detect the character encoding used in a Web document, the user may be presented with unreadable text. This information is particularly important for those maintaining and extending a multilingual site, but declaring the character encoding of the document is important for anyone producing XHTML/HTML or CSS. This tutorial will give you an understanding of the topic that will help you make the right choices when doing so. The topic is not as straightforward as it may sometimes appear, and the advice contained here is the end result of a great deal of thought and discussion.

http://www.w3.org/International/tutorials/tutorial-char-enc/