UU can refer to several things:

• Unitarian Universalism
• NYSE stock ticker symbol for United Utilites
• the Unseen University (in the novels of Terry Pratchett)
• Utrecht University, Netherlands
• University of Ulster, Northern Ireland
• University of Utah, United States
• Union University, United States
• Uppsala Universitet, Sweden
• UUNET (Internet Service Provider commonly referred to as 'UU')