AD> This book examines the structure and function of the English it-cleft configuration from within the framework of construction grammar. It defends a straightforward extraposition-from-NP analysis (on which the cleft clause is a restrictive relative, modifying the initial it) and claims that all types of it-cleft involve nominal predication. Support for this analysis comes from three main areas: (a) the central role of definiteness in the creation of specificational meaning, (b) the existence and makeup of predicational (and proverbial) it-clefts, and (c) the early, historical it-cleft data. In addition, the book contains a sizeable diachronic component, drawing data from the Penn Parsed Corpora of Historical English and from the International Corpus of English - Great Britain. This investigation informs and advances what is an otherwise simple account of the English it-cleft, explaining how and why the configuration has developed an assortment of peculiar, construction-specific properties over time.