This book addresses the European Court of Human Rights' fairness standards in criminal appeal, filling a gap in this less researched area of studies. Based on a fair trial immediacy requirement, the Court has found several violations of Article 6 of the European Convention on Human Rights at the appellate level by at least eighteen States of the Council of Europe in a vast array of cases, particularly in contexts of first instance acquittals overturning and of sentences increasing on appeal. On the one hand, the book critically engages this case-law with the law revisions it has recently inspired in European countries, as well as with the critiques and difficulties that it continues to raise. On the other hand, it interweaves insight from criminal procedure theory with new discoveries in the field of cognitive sciences (neuroscience of memory, philosophy of knowledge, AI), shedding an interdisciplinary light on the (in)adequacy and limits of the Strasbourg Court's jurisprudence.