This document discusses hub sites in Office 365 and SharePoint Online. It begins by explaining what hub sites are and their purpose of aggregating related team and communication sites. It then covers basics of hub sites like how they bring together sites, provide cross-site navigation and search, and apply a consistent look and feel. The document also discusses creating hub sites, associating other sites to hubs, navigation, search, branding and theming when using hub sites. It provides examples of common use cases for hub sites and known current limitations. It concludes by referencing additional resources on advanced hub site uses.