Interest in the content of this book has developed out of an examination of the prompter who operated in full view of the audience and offered all the lines to the players. In 2001 at Groningen a production of the Towneley Second Shepherds’ Play focused on an examination of this convention. Many of the audience responses then were concerned with the figure of the prompter as he was seen to operate simultaneously both 'inside' and 'outside' the action of the play. Such a role and its function is fascinating, not only in its own right, but also in relation to how it might inform us about the nature and purpose of presented theatre. The ability of such a figure to move in and out of the action, and thus different realities, characterizes a relationship to the action and the audience. The same fascination exists in relation to roles of the narrator and the expositor. Sometimes these roles are overt ones; sometimes they 'double up' with roles of actors, personages or characters. These figures are of pivotal significance in the communication of those plays in which they operate. The purpose of this book is to investigate the nature of these roles in order to identify their influence upon the performance of medieval plays.