A mashup is a web application that combines data from multiple sources to create a new integrated application. Mashups are enabled by recent web technologies like Ajax, REST, XHTML, CSS and RSS that allow data to be dynamically pulled from different sources and presented in a unified way. While similar to earlier concepts like web portals and aggregators, mashups uniquely generate new information and experiences from existing data sources. Legal and business issues remain regarding rights to use third-party data and reliance on external data sources.