Can OUGHT be derived from IS? This book presents a systematic investigation of this time-honored philosophical problem by means of modern alethic-deontic predicate logic. Two comprehensive introductory chapters into the philosophical and logical foundations make the text understandable also for non-logicians ethicists, social scientists and students of philosophy. New in this study are two leitmotifs: relevance and metalogical generality. It turns out that is-ought inferences indeed exist, but they are all irrelevant in a precise logical sense. New proof techniques allow to establish this result for very broad classes of logics. A profound philosophical investigation of the question of analytical or strongly intersubjective is-ought bridge principles supplements the logical study. The final results imply incisive limitations for the justifiability of ethics as opposed to empirical science.