This edition in the IFA Seminar Series contains the lectures of a seminar held in Cancun, Mexico in 1992 during the 46th Congress of the International Fiscal Association on the theory and practice of advance ruling in the fiscal sphere. Advance ruling may be defined as 'a decision regarding the consequences of a proposed transaction, given by the competent authority and binding upon that authority'. The subject, applied to the field of taxation, is regarded by different authors from the perspectives of France, Germany, The Netherlands, Sweden and the USA. The situation with respect to the practice and legality of advance ruling in fiscal matters differs in the various countries. In some countries the advance settlement of tax questions is more common than in others. In the Netherlands, for example, there is a long standing tradition of the advance settlement of tax questions creating a great deal of certainty about the tax consequences of certain commercial activities long before the assessment is actually made. Despite the differences existing in the USA, France, The Netherlands, Germany and Sweden with regard to advance ruling in tax matters a few general characteristics can be given. In all the countries in question the tax payer does not, in all cases, have a right to an Advance Ruling, but in case he does obtain one, it is binding upon the tax authorities. Finally the tax payer in all the countries concerned can renounce the right to rely on an Advance Ruling.