This book looks at various important events relating to the poetics of light in theatre production in the West in the twentieth century, from the great reformists at the beginning of the century to contemporary artists such as Josef Svoboda, Alwin Nikolais and Robert Wilson. The intention isn’t to outline a somewhat comprehensive history of stage lighting, instead it is an attempt to identify some basic issues concerning its use. Lighting issues are unshackled from the limited contexts of technique and image, where they often end up only to be relegated, and examined in the context of the performance’s space/time structure, poetic and dramatic construction, and the relationship with the performer. A section dedicated to the theatrical work of the author outlines the distinctive point of view behind the book, regarding the creative processes and the operational relationship with technique. The title Active Light is a direct reference to Adolphe Appia who, at the end of the nineteenth century, was one of the first to deal with the issue of light explicitly as an artistic issue in theatre, with his own writings and creations. As far as Appia was concerned lumière active was expressive light, creating shapes, forming poetic matter and dramatic substance.