This book comprises the final reports of the annual meeting of the European Association of Tax Law Professors (EATLP) held in Leuven, Belgium from 27-29 May 2010. The main subject of the conference was retroactivity in taxation.rnrnMain contentsrnGeneral reportrnrnSpecial topicsrn-Legal certainty: a matter of principlern-Retroactive and retrospective tax legislation: a principle based approach; a theory about ??riority principles of transition law??and ??he method of the catalogue of circumstances??n-Retroactive interpretative statutes and validation statutes in tax law: an assessment in the light of legal certainty, separation of powers and the right to a fair trialrn-Legislation by press release: the role of announcements in the debate about retroactive tax legislationrn-The law and economics approaches to retroactive tax legislationrn-It?? the outcomes, not the rules ??transition issues in the process of tax reformrnrnNational reportsrnAustria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Luxembourg, Netherlands, Poland, Portugal, Spain, Sweden, Turkey, United Kingdom, United States