Complementizers may be defined as conjunctions that have the function of identifying clauses as complements. In recent years, it has become increasingly clear that complementizers may have additional functions. Some of these additional functions may be characterized as pragmatic. For instance, omissible complementizers like English that may serve as pause markers or as signals of genre or social level. Other functions are semantic in the sense that they represent conventional contributions to the meanings of the complements. The present book is concerned with semantic complementizer functions.