This reprint of the 4th edition of the "Blue Book" contains the toxicological evaluation of 899 flavouring substances classified according to their chemical structure and divided into substances which may be added to food for human consumption without hazard to public health and flavouring substances that are temporarily acceptable in foodstuffs, that is to say, those for which there does not exist enough toxicological data for a definite safety-in-use assessment. Safety-in-use criteria are recommended which should be met by the manufacturers of flavouring substances. Also included are the five modifications to the 4th edition (1992) so far adopted by the Committee of Experts on Flavouring Substances of the Council of Europe.