It has become something of a commonplace in theatre studies to state that the spectator is at the centre of the theatrical event and hence of theatre itself. On one level, the statement is self-evident: a theatrical performance without an audience is at best a rehearsal, at worst a hypothetical construct. Few scholars today would argue against the proposition. Claims regarding the spectator's centrality are ubiquitous in most fields of theatre studies: they figure in performance analysis as well as theatre theory and history. This assumed centrality is not, however, matched by a corresponding quantity of research. As the annotated bibliography at the end of this chapter indicates, major books on the subject can be counted on the fingers of one hand. There are a number of reasons for this. The most important is that theatre studies by tradition has defined itself, like literature or art history, as a discipline investigating an aesthetic object: initially the drama, then the theatrical performance. As we shall see in different sections of this book, there are many different ways to investigate this object: all the different interpretive strategies elaborated by the humanities to study texts, images and musical scores can and have been applied to theatre as well.