This book focuses on current theoretical and empirical research into countability in the nominal domain, and to a lesser extent in the verbal domain. The presented state-of-the-art studies are situated within compositional semantics combined with the theory of mereology, and draw on a wealth of data, some of which have hitherto been unknown, from a number of typologically distinct languages. Some contributions propose enrichments of classical extensional mereology with topological and temporal notions as well as with type theory and probabilistic models. The book also presents analyses that rely on cutting-edge empirical research (experimental, corpus-based) into meaning in language. It is suitable as a point of departure for original research or material for seminars in semantics, philosophy of language, psycholinguistics and other fields of cognitive science. It is of interest not only to a semanticist, but also to anybody who wishes to gain insights into the contemporary research into countability.