This book is the result of over 15 years of collaborative research on Jurassic and Early Cretaceous Radiolaria. During this time span, radiolarian literature has at least doubled and for the Mesozoic, the number of modern publications grew from a handful in 1978 to over one thousand. This book is a synthesis of our knowledge on Middle Jurassic - Early Cretaceous radiolarians, that has been created in collaboration with ail the colleagues that appear in the list of contributors. However, many decisions concerning the final systematic choices, the weighting of prime data for biochronology, and the final presentation were taken by the Lausanne group in the last two years prior to publication. The aim of this foreword is to briefly state the objectives and the limitations of our work. When we started out in 1989, we were perhaps much Jess aware of these limitations. lt was during the countless calculations that led to the zonation presented in this book that we learned most about these limitations. The second part of this foreword talks about the organisation of this book, which is governed much more by practical than by theoretical aspects.