The World Wide Web is still developing very quickly. The basic components HTML and HTTP are slowly stabilizing while new formats such as XML (eXtensible Markup Language; for general markup) and CSS (Cascading Style Sheets; for styling information) are being used more and more. In this quickly moving environment, internationalization (i18n) is important to make sure that all users worldwide can equally benefit from Web technology. The Web can be considered a single application, all parts of which must work together regardless of country, language, etc. This tutorial will give an introduction to internationalization on the World Wide Web. A central part is the Unicode-based Reference i18n Model, which appeared first in HTML and has now made its way in XML, CSS and more. It will be described in detail with particular emphasis on HTML and CSS. The tutorial also addresses language tagging, bidirectionality, multilingual typography and advanced applications. A section is devoted to the design and implementation of multilingual Web sites, discussing localization issues, language negotiation and other aspects.