CIU may refer to:

• Cédula de Identidad de Uruguay, the Uruguayan identity card
• Convergència i Unió, a Catalan political party
• Crash Investigation Unit, an Australian factual television program
• Working Men's Club and Institute Union, an association of social clubs in the United Kingdom
• Chippewa County International Airport in Sault Ste. Marie, Michigan (IATA Code: CIU)
• Columbia International University, a Bible college and seminary in Columbia, South Carolina
• Cyprus International University, Cyprus, North Cyprus
• Cape plc, a construction company listed in the Alternative Investment Market under ticker CIU
• Customs and Immigration Union (Canada)
• Chronic idiopathic urticaria, also known as hives
• Collective investment undertaking, another term for an investment fund

• Athletics at the 2014 Commonwealth Games – Men's hammer throw
• Athletics at the 2014 Commonwealth Games – Men's high jump
• Athletics at the 2014 Commonwealth Games – Men's javelin throw
• Athletics at the 2014 Commonwealth Games – Men's long jump
• Athletics at the 2014 Commonwealth Games – Men's marathon
• Athletics at the 2014 Commonwealth Games – Men's pole vault
• Athletics at the 2014 Commonwealth Games – Men's shot put
• Athletics at the 2014 Commonwealth Games – Men's triple jump
• Athletics at the 2014 Commonwealth Games – Women's 10,000 metres
• Athletics at the 2014 Commonwealth Games – Women's 100 metres
• Athletics at the 2014 Commonwealth Games – Women's 1500 metres
• Athletics at the 2014 Commonwealth Games – Women's 200 metres
• Athletics at the 2014 Commonwealth Games – Women's 400 metres
• Athletics at the 2014 Commonwealth Games – Women's 5,000 metres
• Athletics at the 2014 Commonwealth Games – Women's 5000 metres
• Athletics at the 2014 Commonwealth Games – Women's 800 metres
• Athletics at the 2014 Commonwealth Games – Women's discus throw
• Athletics at the 2014 Commonwealth Games – Women's hammer throw
• Athletics at the 2014 Commonwealth Games – Women's heptathlon
• Athletics at the 2014 Commonwealth Games – Women's high jump
• Athletics at the 2014 Commonwealth Games – Women's javelin throw
• Athletics at the 2014 Commonwealth Games – Women's long jump
• Athletics at the 2014 Commonwealth Games – Women's marathon
• Athletics at the 2014 Commonwealth Games – Women's pole vault
• Athletics at the 2014 Commonwealth Games – Women's shot put