A libretto is an indispensable part of an opera as a musical genre: with few exceptions, operas have been the subject of musicological studies, and instrumental versions of sung or unsung opera numbers may be heard, but we never listen to libretto texts being performed without the music. Thus as a literary form the libretto is a highly specific genre with its own particular attributes. This volume offers an approach to the libretto through the discussion of these attributes in many different examples. It explores what may be expected of a librettist in response to the demands of the genre’s characteristics, his trials and tribulations, his exchanges with the composer while adapting or converting a source, almost always a literary source, into the eventual libretto, and about the different musical ways of dealing with the text. In this way the volume clarifies the fundamental differences between the libretto and other literary genres.