Theatre design, the art and technique of designing and building a space—a theatre—intended primarily for the performance of drama and its allied arts by live performers who are physically present in front of a live audience. As an art form, theatre does not require a purposefully designed building in which to be presented. But when audiences gather regularly to experience a performance, attempts are generally made to organize the space in order to improve on the nature of the experience the audience can have, and this is the beginning of theatre design. The simplest theatres are cleared areas of ground around which people can stand or sit to view a performance. Theatre design, however, is concerned with elaborating such space—first, to provide the optimum conditions for the audience to experience a theatre performance and, second, to aid the performers in achieving the fullest expression of their art.

The practice of theatre design can encompass open-airspaces or spaces that are fully enclosed. It can involve a temporary structure put up only on certain occasions or a complete stand-alone permanent building. It can include purpose-built areas within larger complexes or the modification of buildings originally built for other purposes. Because they are well designed for the gathering of a group of people and generally allow for controlled access, theatres tend to be used as multipurpose buildings that can provide assembly space for lectures, meetings, concerts, films, performance art, circuses, and even certain types of sporting events. But at its most basic level, a theatre provides a space for the performers to enact their performance and a space for the audience to experience that enactment. The space used for performance is most often referred to by the word stage in English. The space occupied by the audience is referred to by a variety of terms, of which auditorium (literally, “hearing place”) may be the most common.