Three general categories of forgeries are discussed: works deliberately created to be sold as the product of another artist, exact replicas of other innocently created pieces which are later sold as originals, and works changed by an artist to enhance value or sales potential. After an introduction to the art forgery problem, various methods for establishing authenticity are considered. Purchasers can help to protect themselves by being familiar with the artist's style, period, and peculiarities and by requiring a certificate of authenticity and a bill of sale for each purchase. Experts can aid in determining a work's authorship or in verifying its age and materials through scientific tests. However, many experts are reluctant to enter into disputes which may lead to court proceedings, and authentication often costs more than the work of art itself. Authentication methods discussed include radiocarbon age determination, in which residual radiocarbon activity is counted to date organic materials between a few hundred and 50,000 years old; thermoluminescent analysis, in which ceramic ware or fired clay is heated to measure the radiation that has accumulated since the original firing; obsidian hydration, in which volcanic crystals (obsidian) are tested to determine the time that has elapsed since carving; the fission tracks technique, in which glassy or crystalline substances containing uranium are examined to measure the destruction caused by this element through time; comparative analysis, in which paints and other substances in original works are analyzed and compared to those in known samples from the same period; the analytical reconstruction of manufacturing techniques, in which period authenticity of materials is tested; and microscopic and X-ray techniques, in which the structures of materials are examined for period authenticity. Existing legislation is discussed in the areas of penal law and buyers' remedies, and other solutions including registration and self-policing are considered. Numerous footnotes are included.