The 18A was a 2013 Argentine protest demonstration.
18A, 18-A, 18a or XVIII-A may also refer to:
Air & Space 18A, a 1965 United States gyroplane Eighteen angstrom, a marketing term for a sub-2 nm process Highway 18A (Ontario) Nevada State Route 18A Soyuz 18a, a 1975 Soviet spacecraft mission Stalag XVIII-A, a German prisoner of war camp Volkswagen Type 18A, a 1949 special version made for the German police