Is authenticity a sham? A widening rift confronts art museum visitors and workers alike, between traditional presentation of artifacts in the name of authenticity and critical comment that recognises it only as a relative and power-laden term. Both points of view are explored here to arrive at a liberating view of art museums. Meanings of authenticity are considered in contemporary society; in historical roles of church and museum in policing the cults of saints and of art; in the practical and conceptual problems of classifying and conserving objects; and in our experience as museum visitors. Mapping and framing emerge as metaphors for what curators do, in an escape from authenticity that opens up new possibilities for art museum practice. On the way there are detailed accounts of evidence in art attribution, and of how it is weighed in scholarly judgements and when art comes to court; of the transformations of works of art through ageing and treatment; of perceptual anomaly as a source of changing meanings in artifacts; and of the framing of experience. The book is aimed at students of museum studies, but raises issues that apply widely in art history.