This book is the first of two volumes devoted to the work of Theo Kuipers, a leading Dutch philosopher of science. Philosophers and scientists from all over the world, thirty seven in all, comment on Kuipers' philosophy, and each of their commentaries is followed by a reply from Kuipers. The present volume focuses on Kuipers' views on confirmation, empirical progress, and truth approximation, as laid down in his From Instrumentalism to Constructive Realism (Kluwer, 2000). In this book, Kuipers offered a synthesis of Carnap's and Hempel's confirmation theory on the one hand, and Popper's theory of truth approximation on the other. The key element of this synthesis is a sophisticated methodology, which enables the evaluation of theories in terms of their problems and successes (even if the theories are already falsified), and which also fits well with the claim that one theory is closer to the truth than another. Ilkka Niiniluoto, Patrick Maher, John Welch, Gerhard Schurz, Igor Douven, Bert Hamminga, David Miller, Johan van Benthem, Sjoerd Zwart, Thomas Mormann, Jesús Zamora Bonilla, Isabella Burger & Johannes Heidema, Joke Meheus, Hans Mooij, and Diderik Batens comment on these ideas of Kuipers, and many present their own account. The present book also contains a synopsis of From Instrumentalism to Constructive Realism. It can be read independently of the second volume of Essays in Debate with Theo Kuipers, which is devoted to Kuipers' Structures in Science (2001).