A'-levels (short for "Advanced level General Certificates of Education") are non-compulsory examinations taken by people in England and Wales at the end of secondary education - typically at age eighteen. The name "A-levels" is also given to the qualifications awarded following these. British universities take predicted A-level results into account when deciding whether to offer places to applicants, and generally make offers of places that are conditional on applicants achieving specific minimum A-level grades. Formerly, "O-level" (Ordinary level) GCE examinations existed, but these were replaced by GCSEs in 1988.

Following changes introduced under Curriculum 2000 in 2001, an A-level now consists of three AS-level modules and three A2-level modules. In many subjects one or two of these six modules take the form of coursework rather than examinations. Completion of three AS modules qualifies a student for an AS-level, and completion of three AS and three A2 modules qualifies him or her for a full A-level. Raw marks for each module are converted to UMS (Uniform Mark Scale) marks, which are totalled to determine a candidate's final grade for each subject. Many students study four subjects to AS-level during the first year of their sixth form studies, take AS exams in these at the end of the first year, and then choose three to continue to A-level during the second year, but practices vary between and within schools. Some students decide the level to which they will study each of their subjects before entering the sixth form. The number of subjects studied also varies, but three subjects studied to A-level are generally a requirement for university applications.