In September 2009, the authors of this book came together in Leiden for a workshop called Days of Judgement . The majority of the chapters presented here are based upon a selection of the talks held at the Leiden workshop. Right from the start, the idea was to show the importance of the history of the notion of judgement for philosophy today. As one may learn from Wayne Martin’s book Theories of Judgment , Cambridge University Press, 2006, the fi eld of judgement is broad, and one needs to give a direction to the topic. The general idea of both the workshop and the book presented here is to take Per Martin-L?f’s constructive type theory as a starting point, because the notion of judgement plays a central role there. Our logical system is not only in need of propositions; it also needs judgements in which propositions are asserted to be true and known. According to Martin-L?f, one is entitled to make a judgement if one has a ground for it. It is thus that the notion of judgement is related to the notions of truth, knowledge and ground. It is precisely the relation between these notions that has given a focus to the topic of the book presented here. The book starts with two chapters that were not part of the workshop. In the fi rst chapter, Martin-L?f gives a clear explanation of the way he understands the notion of judgement, and he relates his position to that of the logical positivists. The fi rst part of the chapter is a reprint from the paper “Veri fi cationism Then and Now”, published in The Foundational Debate (W. DePauli-Schimanovich et al. (eds.). Dordrecht: Kluwer, 1995, 187–196). Martin-L?f has added to the paper a postscript , in which he makes an amendment to the paper. G?ran Sundholm was asked to write an afterword to his paper “Constructions, Proofs and the Meaning of the Logical Constants”, which appeared in 1983 in the Journal of Philosophical Logic (volume 11: 151–172). In this afterword, the second chapter here, Sundholm gives an overview of the history of constructive type theory of the last 30 years, focusing on the notions of construction, demonstration and judgement and the ambiguities in these notions. This afterword may help the reader to fi nd the important literature that appeared on the notion of judgement within constructive type theory.