Domesticated animals formed an important element of farming practices in prehistoric Britain, a fact revealed through the quantity and variety of animal bone typically found at archaeological sites. However, it is not known whether the ruminant animals were raised purely for their tissues (e.g., meat) or alternatively were exploited principally for their milk. Absorbed organic residues from pottery from 14 British prehistoric sites were investigated for evidence of the processing of dairy products. Our ability to detect dairy fats rests on the observation that the delta(13)C values of the C(18:0) fatty acids in ruminant dairy fats are approximately 2.3 per thousand lower than in ruminant adipose fats. This difference can be ascribed to (i) the inability of the mammary gland to biosynthesize C(18:0); (ii) the biohydrogenation of dietary unsaturated fatty acids in the rumen; and (iii) differences (i.e., 8.1 per thousand ) in the delta(13)C values of the plant dietary fatty acids and carbohydrates. The lipids from a total of 958 archaeological pottery vessels were extracted, and the compound-specific delta(13)C values of preserved fatty acids (C(16:0) and C(18:0)) were determined via gas chromatography-combustion-isotope ratio mass spectrometry. The results provide direct evidence for the exploitation of domesticated ruminant animals for dairy products at all Neolithic, Bronze Age, and Iron Age settlements in Britain. Most significantly, studies of pottery from a range of key early Neolithic sites confirmed that dairying was a widespread activity in this period and therefore probably well developed when farming was introduced into Britain in the fifth millennium B.C.