Web 2.0 refers to more interactive and user-driven websites that allow users to contribute content. Key characteristics include users owning and controlling data on sites through rich interfaces. While some criticize that Web 2.0 is not new, sites like Amazon and eBay allowed reviews since 1995. Social networking sites emerged, allowing users to share and communicate information in different ways. Review sites also emerged, growing rapidly since Web 2.0, allowing users to write product reviews to aid others' purchasing decisions.