ACU may refer to:

• IATA airport code for Achutupo Airport in Guna Yala Region, Panama

• Address computation unit, another name for address generation unit
• Automatic Client Upgrade, a facility within the Novell Open Enterprise Server

• Abilene Christian University, a private Christian university located in Abilene, Texas
• Adichunchanagiri University, a private university located in Karnataka, India
• Ahram Canadian University, a private Egyptian university located in 6th of October City, Giza, Egypt
• Ajayi Crowther University, a private Christian university located in Oyo, Oyo State Nigeria
• American City University in California or Wyoming
• Arizona Christian University, a private Christian university located in Phoenix, Arizona
• Association of Commonwealth Universities, an association that represents over 480 universities from Commonwealth countries
• Australian Catholic University, Australia's only public Catholic university

• Açu, municipality in the state of Rio Grande do Norte, Brazil
• Açu River, another name for the Piranhas River in Brazil
• Pariquera-Açu, a municipality in the state of São Paulo in Brazil
• Superporto do Açu, an industrial port complex in the state of Rio de Janeiro in Brazil

• Acu Publishing, an imprint of the German group VDM Publishing devoted to the reproduction of Wikipedia content
• Altura Credit Union, a credit union in California
• American Conservative Union, a political lobbying group in the US
• Arab Customs Union, an organization under the Arab League for a Customs Union between Arab Members of the League
• Asian Clearing Union, an organization that settles international payments between member countries
• Assiniboine Credit Union, a credit union in Manitoba
• Auto-Cycle Union, the governing body of motorcycle sport in Great Britain
• American Coalition for Ukraine, a coalition of organizations that advocate for US support of Ukraine's defence and sovereignty

• Army Combat Uniform, the combat uniform worn by the US Army, US Air Force, and US Space Force
• Assault Craft Unit, military units of the US Navy that specialize in amphibious warfare

• Auto-Cycle Union, an officially recognised motorcycle governing body of the UK
• Automovil Club del Uruguay, a member of the Fédération Internationale de l'Automobile

• ACU, a codon for the amino acid threonine
• ACU (Utrecht), a music venue in Utrecht, the Netherlands
• Armored Command Unit, the key unit in the RTS video game Supreme Commander
• Asian Currency Unit, a proposed unit of currency for Asia and Oceania
• Assassin's Creed Unity, a game set during the French Revolution