The commitment to peer review as a basis for judging science is deeply rooted in academic culture, and has been largely accepted in the UK's £2 billion annual public funding of science. Yet the criteria are insufficiently transparent for public accountability. In practice peer review focuses on three concerns. ‘Fitness for purpose’ relates to the means to be used in the science — if unfit, the science is invalid, certainly not worth funding. ‘Knowledge added’ relates to the ways in which and the degree to which the science may add to the existing stock of knowledge — all science worth funding should offer some gain. ‘Value for money’, where the value is assessed as knowledge-added, is the appropriate criterion for making choices with limited budgets. This three-stage decision algorithm can demystify and defend peer-review practice. Copyright , Beech Tree Publishing.