What is text understanding? It is the dynamic process of constructing coherent representations and inferences at multiple levels of text and context, within the bottleneck of a limited-capacity working memory. The field of text and discourse has advanced to the point where researchers have developed sophisticated models of comprehension, and identified the particular assumptions that underlie comprehension mechanisms in precise analytical or mathematical detail. The models offer a priori predictions about thought and behavior, not merely ad hoc descriptions of data. Indeed, the field has evolved to a mature science. The contributors to this volume collectively cover the major models of comprehension in the field of text and discourse. Other books are either narrow -- covering only a single theoretical framework -- or do not focus on systematic modeling efforts. In addition, this book focuses on deep levels of understanding rather than language codes, syntax, and other shallower levels of text analysis. As such, it provides readers with up-to-date information on current psychological models specified in quantitative or analytical detail.