This is a general account of the different aspects of art forgery and its detection. Several classic cases are mentioned, together with the use of radiography as a means of investigation. The use of radioactive methods of dating are mentioned, particularly with references to the authentification of oil paintings. Non-destructive methods of analysis, such as x-ray fluorescence and neutron activation, are mentioned and case histories of their use are cited. The bulk of the article deals with the author's own work on the analysis of medieval gold coins of the Kingdom of Sicily by both neutron activation and specific gravity analysis. The results showed that the coinage conformed to the theoretical composition, and was not officially debased, as has been suggested. -- AATA