Following the introduction of Curriculum 2000 in September 2000 (with the first AS-level examinations held in Summer 2001 and A2 examinations the following year), an A-level now consists of six units studied over two years. Normally, three units are assessed at the end of the first year, and make up a stand-alone qualification called the "AS-level" (or Advanced Subsidiary level). Another three modules are assessed at the end of the second year, which make up the "A2". A2 units do not form a qualification in their own right; the satisfactory completion of the AS and A2 units in the same subject is required to constitute a complete A-level.

Units are assessed by exam papers marked by national organisations and internally-assessed coursework. Four organisations set and mark exam papers in England (AQA, Edexcel and OCR).

While A-levels are a qualification in their own right, they are often the prerequisite for university-level study as well, making them a de facto university entrance examination (though certain universities also require applicants to take separate entrance examinations). Universities in the United Kingdom frequently demand that applicants achieve a minimum set of grades in A-level examinations, or the equivalent in other examination systems, before accepting them.