Wikis provide flexible ways for supporting the quick and simple creation, sharing and management of content. Despite the obvious benefit of a wiki, its contents are barely machine interpretable. Structural knowledge, for example about how concepts are interrelated, can neither be formally stated nor be automatically processed. In addition, numerical data is available only as plain text and thus cannot be processed by its actual meaning. Semantic Wikis provide the ability to capture (by humans), store and later identify (by machines) further meta-information or metadata about those articles and hyperlinks, as well as their relations. Semantic Web provides intelligent access to heterogeneous, distributed information, enabling software products (agents) to mediate between user needs and the information sources available. This chapter describes the use of semantic technologies in wiki.