ACAS or Acas may refer to:

Aviation

• Airborne collision avoidance system, an International Civil Aviation Organization standard
• Assistant Chief of the Air Staff, a senior appointment in the Royal Air Force

Other uses

• Aboriginal Children's Advancement Society, an organization in New South Wales
• Acas (Advisory, Conciliation and Arbitration Service), an independent non-departmental public body of the Government of the UK
• Acâș, a commune in Satu Mare County, Romania
• Acas District, Ocros, Peru
• Associate in the Casualty Actuarial Society, a level of membership in the Casualty Actuarial Society
• Assured Compliance Assessment Solution, a tool that automatically identifies configuration vulnerabilities on United States Department of Defense computer systems